Liquid crystal display device

ABSTRACT

A liquid crystal display device of the present invention is composed of a λ/4 plate  1 , a λ/2 plate  2 , and a polarizing plate  3  which are provided in this order from the side of a liquid crystal layer  10 . Here, an angle formed between an absorption axis of the polarizing plate  3  and an absorption axis of the λ/2 plate  2  is about 45°, an in-plane retardation of the λ/2 plate  2  is set to a value obtained by adding λ/4 to an in-plane retardation of a retardation plate  1 , desirably, the λ/4 plate  1 , and an optical axis of the λ/4 plate  1  and an optical axis of the λ/2 plate  2  are orthogonal to each other. In this configuration, the optical axis of the λ/4 plate  1  is placed at 150°, the optical axis of the λ/2 plate  2  is placed at 60°, and the absorption axis of the polarizing plate  3  is placed at 15°. This configuration improves display characteristics, that is, performs bright display at a higher contrast ratio and in a wider viewing angle with less dependence on visual field, thereby realizing an excellent reflection-type liquid crystal display device that is very easy to view even in a relatively dim place such as an indoor environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2002-332601, filed on Nov. 15,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflection-type liquid crystaldisplay device for use in low power consumption devices such as aportable terminal and the like.

2. Description of the Related Art

A reflection-type liquid crystal display device performs display bytaking environmental light such as interior illumination or sunlightthereinto and reflecting it by a reflector to the observer side. Thisreflection-type liquid crystal display device has low power consumptionbecause of no need for a backlight and is in wide use for a portableterminal, PDA, and so on.

The reflection-type liquid crystal display device has low powerconsumption because of performance of display through use ofenvironmental light as described above, but tends to be relativelyinferior in display characteristics such as a contrast ratio, viewingangle, and so on. Hence, the following measures are considered toimprove the display characteristics.

(Measure 1)

A reflection-type liquid crystal display device is proposed which uses avertical alignment-type liquid crystal display panel since it canrealize a high contrast ratio and high reflection intensity. As shown inFIG. 45A, a quarter-wave (λ/4) plate 101 is arranged here above a frontsurface of the vertical alignment-type liquid crystal display panel, andblack display is performed where the application voltage is turned off.

Regarding this λ/4 plate 101, such a technique is also proposed that theplate is composed of two plates, that is, a half-wave (λ/2) plate 103and a λ/4 plate 104 as shown in FIG. 45B to reduce wavelength dispersionof birefringence thereof. Note that only a reflecting electrode, aliquid crystal layer, and a transparent electrode are shown representinga liquid crystal panel in FIGS. 45A and B for convenience.

A liquid crystal molecule substantially vertically stands in a statewhere no voltage is applied to enable realization of ideal blackdisplay. Besides, in a state where voltage is applied, when a practicalretardation of the liquid crystal layer becomes λ/4, white display isperformed. In this reflection-type liquid crystal display device, it iseffective to provide a negative retardation plate 102 between the liquidcrystal panel and the λ/4 plate 101 in order to improve viewing anglecharacteristics. The existence of the negative retardation filmcompensates the retardation of the liquid crystal layer.

(Measure 2)

In the case in which environmental light is reflected by a reflector tothe observer side, when the reflector is composed of a smooth mirrorsurface, display becomes bright in a regular reflection region andbecomes dark in other regions, leading to great dependence on viewingangle, and the display in the regular reflection region may havemetallic luster. Hence, such there is a known technique in whichprojections and depressions in dot-like plane shapes are formed on thesurface of a reflector to disperse reflection light, thereby realizingdisplay with less dependence on viewing angle and no metallic luster(see Patent Document 1).

Further, a twisted nematic (TN) mode using one polarizing plate (seePatent Document 2) is proposed as a display mode. TN mode is such a modethat liquid crystal having a positive dielectric constant anisotropy istwist-aligned in a horizontal direction, in which incident environmentallight is converted into linearly polarized light by a polarizing platefor white display where no voltage is applied by rotating itspolarization azimuth 180° by a retardation plate having a retardation ofabout a quarter of the visible light wavelength and a liquid crystallayer, and for black display where voltage is applied by rotating thepolarization azimuth 90° by the retardation plate having a retardationof about a quarter of the visible light wavelength.

(Patent Document 1)

Japanese Patent Application Laid-Open No. Hei 6-175126

(Patent Document 2)

Japanese Patent Application Laid-Open No. Hei 6-11711

(Patent Document 3)

Japanese Patent Application Laid-Open No. Hei 11-311784

(Patent Document 4)

Japanese Patent Application Laid-Open No. Sho 60-256121

(Patent Document 5)

Japanese Patent Application Laid-Open No. Sho 62-210423

(Patent Document 6)

United Kingdom Patent Specification No. 1,462,978

(Patent Document 7)

Japanese Patent Application Laid-Open No. Hei 10-153802

(Patent Document 8)

Japanese Patent Application Laid-Open No. 2001-4999

(Patent Document 9)

Japanese Patent Application Laid-Open No. 2000-35570

(Patent Document 10)

Japanese Patent Application Laid-Open No. 2000-171788

(Patent Document 11)

Japanese Patent Application Laid-Open No. 2001-154190

(Patent Document 12)

Japanese Patent Application Laid-Open No. Hei 6-337421

(Non-Patent Document 1)

The journal of the Institute of Television Engineers of Japan Vol. 50,No. 8, pp 1091-1095, 1996

However, the above-described measures for improvement of displaycharacteristics have problems as follows:

In the case of the measure 1, production of the negative retardationfilm requires a special and very advanced technique, such as, stretchingof an optical film in two directions, or application of a specialoptical substance onto a film being a base, and thus the negativeretardation plate is expensive.

A technique for easily realizing this negative retardation film isproposed by Tohoku University. This is produced by layering uniaxiallystretched films each having a desired negative retardation and anin-plane retardation the same as the negative retardation which areorthogonal. This case, however, needs many films, leading to a problemthat the display becomes thick or expensive.

In the case of the measure 2, liquid crystal anchoring to the interfaceof a substrate still remains without switching after application ofvoltage in the TN mode, leading to a problem that black luminance floatsand thus a sufficient contrast ratio cannot be obtained. The visibilityof display is defined by the brightness and contrast ratio, in whichdisplay is easy to view even at a low contrast ratio if it is bright,while display needs to have a high contrast ratio if it is dark (seeNon-Patent Document 1). The reflection-type liquid crystal displaydevice performs display by taking environmental light thereinto andreflecting it by a reflector to the observer side, and therefore thedisplay is dark in an indoor environment and insufficient in contrastratio to become hard to view.

As means for improving the contrast ratio, proposed is a technique forcompensating black display by substantially matching a slow axis of aretardation plate with an anchoring azimuth of the liquid crystal layer,and decreasing the retardation of the retardation plate by a retardationremaining in the liquid crystal layer (residual retardation) (see PatentDocument 3). The technique has, however, problems that a sufficientcontrast ratio cannot be obtained because of colored black display dueto wavelength dispersion of the liquid crystal layer greater than thatof the retardation plate, and that since the retardation of the liquidcrystal layer needs to be increased by the decreased retardation forwhite display, the driving voltage should be increased to obtain thesame contrast ratio.

SUMMARY OF THE INVENTION

The present invention is made in consideration of the above problems,and its object is to improve display characteristics, that is, torealize bright display at a higher contrast ratio and in a wider viewingangle with less dependence on visual field, so as to provide anexcellent reflection-type liquid crystal display device that is veryeasy to view even in a relatively dim place such as an indoorenvironment.

As a result of earnest studies, the present inventor has devised variousaspects described below.

A liquid crystal display device of the present invention comprises: areflecting layer for reflecting incident light; a liquid crystal layerprovided on the reflecting layer; and an optical compensation plateprovided on a front surface of the liquid crystal layer, wherein theoptical compensation plate has a layer structure constituted of a firstretardation plate, a second retardation plate, and a polarizing platefrom a side close to the liquid crystal layer, and wherein the first andsecond retardation plates have uniaxial anisotropies respectively, andboth are superposed to create, in a combined manner, a function of aquarter-wave plate and a function of a negative retardation plate.

A liquid crystal display device of the present invention comprises: areflecting layer for reflecting incident light; a liquid crystal layerprovided on the reflecting layer, in which alignment of liquid crystalmolecules is vertical; and a retardation plate and a polarizing plateprovided on a front surface of the liquid crystal layer, wherein thereflecting layer has projections and depressions formed on a surfacethereof, an average tilt angle of the projections and depressions beinga value of not less than about 4° nor greater than about 6°, and whereinthe retardation plate has a negative refractive index anisotropy in avertical direction to a surface thereof, a ratio between a retardationRf thereof and a retardation Rlc of the liquid crystal layer, Rf/Rlc,being a value of 0.6 to 0.9.

In this case, in another aspect of the present invention, the reflectinglayer has projections and depressions formed on a surface thereof, anaverage tilt angle of the projections and depressions being a value ofnot less than about 10° nor greater than about 15°, and the retardationplate has a negative refractive index anisotropy in a vertical directionto a surface thereof, a ratio between a retardation Rf thereof and aretardation Rlc of the liquid crystal layer, Rf/Rlc, being a value ofnot less than 0.4 nor greater than 0.7.

In this case, in another aspect of the present invention, the reflectinglayer has projections and depressions formed on a surface thereof, anaverage tilt angle of the projections and depressions being a value ofnot less than about 7° nor greater than about 9°, and the retardationplate has a negative refractive index anisotropy in a vertical directionto a surface thereof, a ratio between a retardation Rf thereof and aretardation Rlc of the liquid crystal layer, Rf/Rlc, being a value ofnot less than 0.5 nor greater than 0.8.

Further, in still another aspect of the present invention, theretardation plate has a retardation of a quarter of a visible lightwavelength in an in-plane direction thereof, and is arranged such thatan angle formed between an azimuth φ in which the reflection intensityis maximum and an absorption axis P of the polarizing plate is a valueof not less than about 65° nor greater than about 90°, and an angleformed between a slow axis F₁ of the retardation plate and theabsorption axis P is about 45°.

Further, in still another aspect of the present invention, theretardation plate has a retardation of a quarter of a visible lightwavelength in an in-plane direction thereof, and is arranged such thatan angle formed between an azimuth φ in which the reflection intensityis maximum and an absorption axis P of the polarizing plate is a valueof not less than about 90° nor greater than about 115°, and an angleformed between a slow axis F₁ of the retardation plate and theabsorption axis P is about 135°.

Further, in still another aspect of the present invention, the liquidcrystal molecules of the liquid crystal layer are aligned such that anangle formed between an azimuth φ in which the reflection intensity ismaximum and a director azimuth L for the liquid crystal molecules is notless than about 45° nor greater than about 90°.

A liquid crystal display device of the present invention comprises: areflecting layer with projections and depressions having azimuthalanisotropies on reflection intensity formed on a surface thereof, forreflecting incident light; a liquid crystal layer provided on thereflecting layer, in which alignment of liquid crystal molecules isvertical; and a quarter-wave plate, a half-wave plate, and a polarizingplate provided in order on a front surface of the liquid crystal layer,wherein respective applicable wavelengths of the quarter-wave plate andthe half-wave plate are made different so that retardations caused bythe quarter-wave plate, the half-wave plate, and the liquid crystallayer due to an oblique incidence or oblique emission in an azimuth inwhich the reflection intensity is maximum are made smaller than theretardations in an azimuth in which the reflection intensity is minimum.The applicable wavelength here refers to a wavelength that causes aretardation of λ/4 or λ/2 by a λ/4 plate or a λ/2 plate.

In another aspect of the present invention, the respective applicablewavelengths of the quarter-wave plate and the half-wave plate are madedifferent by a value of not less than 20 nm nor greater than 200 nm.

Further, in still another aspect of the present invention, theapplicable wavelength of the quarter-wave plate is made smaller than theapplicable wavelength of the half-wave plate.

Further, in still another aspect of the present invention, there furtherprovided is a negative retardation plate between the liquid crystallayer and the quarter-wave plate, wherein the applicable wavelength ofthe quarter-wave plate is made larger than the applicable wavelength ofthe half-wave plate.

Further, in still another aspect of the present invention, there furtherprovided is another half-wave plate between the half-wave plate and thepolarizing plate, wherein slow axes of the quarter-wave plate and thehalf-wave plate are substantially orthogonal, and the applicablewavelength of the half-wave plate is made larger than the applicablewavelength of the other half-wave plate.

According to the present invention, it becomes possible to improvedisplay characteristics, that is, to perform bright display at a highercontrast ratio and in a wider viewing angle with, less dependence onvisual field, so as to realize an excellent reflection-type liquidcrystal display device that is very easy to view even in a relativelydim place such as an indoor environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view for explaining a principle configuration 1in a main point 1 of the present invention;

FIG. 2A and FIG. 2B are perspective views for explaining the principleconfiguration 1 in the main point 1 of the present invention;

FIG. 3 is a perspective view for explaining a principle configuration 2in the main point 1 of the present invention;

FIG. 4 is a perspective view for explaining a principle configuration 1in a main point 4 of the present invention;

FIG. 5 is a perspective view for explaining a principle configuration 2in the main point 4 of the present invention;

FIG. 6 is a perspective view for explaining a principle configuration 3in the main point 4 of the present invention;

FIG. 7 is a cross-sectional view showing a schematic configuration of areflection-type liquid crystal display device of a first embodiment;

FIG. 8A and FIG. 8B are cross-sectional views showing schematicconfigurations of the reflection-type liquid crystal display device ofthe first embodiment;

FIG. 9 is a characteristic diagram showing front contrast dependencewhen the in-plane retardation of a λ/4 plate deviates from apredetermined value;

FIG. 10 is a characteristic diagram showing front contrast dependencewhen the in-plane retardation of a λ/2 plate deviates from apredetermined value;

FIG. 11 is a characteristic diagram showing an optimal angle of apolarizing plate to allow visual angle characteristics vertically andlaterally symmetrical;

FIG. 12 is a schematic diagram showing a method for estimating theretardation of a liquid crystal layer where no voltage is applied andthe retardation of a retardation plate;

FIG. 13 is a schematic diagram showing a method for estimating theretardation of a liquid crystal layer where no voltage is applied andthe retardation of a retardation plate;

FIGS. 14A, 14B, 14C and 14D are schematic diagrams showing a method forfinding a refractive index anisotropy when light is incident, tilting θfrom a Z-axis, on a liquid crystal and a retardation plate;

FIG. 15 is a perspective view schematically showing a configuration ofan optical compensation plate used in a second embodiment;

FIG. 16 is a perspective view showing a configuration of a singlepolarizing plate and a measurement method;

FIG. 17 is a characteristic diagram showing azimuth anglecharacteristics of the single polarizing plate;

FIG. 18 is a perspective view showing a configuration of a polarizingplate+λ/4 and a measurement method;

FIG. 19 is a characteristic diagram showing azimuth anglecharacteristics of the polarizing plate+λ/4;

FIG. 20 is a characteristic diagram showing azimuth anglecharacteristics, for every incident angle, of the reflection intensitymeasured with the incident angle and the azimuth angle varied;

FIG. 21 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 90°, and the incident angle and therotation angle of the axis placement were varied;

FIG. 22 is a characteristic diagram showing azimuth anglecharacteristics of the reflection intensity measured when the axisplacement was rotated +15°, and the azimuth angle of a 30° incidence wasvaried;

FIG. 23 is a characteristic diagram showing azimuth anglecharacteristics of measured contrast ratio (CR);

FIG. 24 is a characteristic diagram showing azimuth anglecharacteristics of the reflection intensity measured when a retardationplate having λ/4 of the visible light wavelength was arranged between apolarizing plate and a reflector such that an angle formed between itsslow axis and absorption axis was 135°, and the azimuth angle of a 30°incidence was varied;

FIG. 25 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 90°, and the incident angle and therotation angle of the axis placement were varied;

FIG. 26 is a perspective view showing a configuration of a polarizingplate+broadband λ/4 and a measurement method;

FIG. 27 is a characteristic diagram showing how the reflection intensitychanges in a directional azimuth with the angle formed between a slowaxis of a λ/2 plate and an absorption axis of a retardation platechanged for every combination of the λ/2 plate and a λ/4 plate;

FIG. 28 is a perspective view showing an axis placement when uniaxiallystretched films are layered;

FIG. 29 is a perspective view showing a configuration of a polarizingplate+λ/4+a compensation plate and a measurement method;

FIG. 30 is a characteristic diagram showing azimuth anglecharacteristics of every compensation plate;

FIG. 31 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 90°, and the incident angle and theangle formed between a slow axis of a uniaxially stretched film and adirectional azimuth were varied;

FIG. 32 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 270°, and the angle formed between anazimuth of liquid crystal alignment and a directional azimuth wasvaried;

FIG. 33 is a schematic view showing a plane shape of a directionalreflector used in a third embodiment;

FIG. 34 is schematic view showing a plane shape of a directionalreflector with slits used in the third embodiment;

FIG. 35A is a characteristic diagram showing azimuth dependence of thereflectance of a polarizing plate+a λ/4 plate;

FIG. 35B is a characteristic diagram showing azimuth dependence of thereflectance of a polarizing plate+a broadband λ/4 plate;

FIG. 36A and FIG. 36B are schematic plane views showing plane shapes ofreflectors used in a fourth embodiment;

FIG. 37 is a characteristic diagram showing azimuth dependence of thereflectance of a reflector;

FIG. 38A is a characteristic diagram showing azimuth dependence ofreflectance (for a non-directional reflector) of a polarizing plate+abroadband λ/4 plate+a liquid crystal layer when the in-plane retardationof a λ/4 plate can be changed between 109 nm and 148 nm;

FIG. 38B is a characteristic diagram showing azimuth dependence ofreflectance (for a directional reflector) of a polarizing plate+abroadband λ/4 plate+a liquid crystal layer when the in-plane retardationof a λ/4 plate can be changed between 109 nm and 148 nm;

FIG. 39A is a characteristic diagram showing azimuth dependence of thereflectance (for a non-directional reflector) of a polarizing plate+abroadband λ/4 plate+a liquid crystal layer when the in-plane retardationof a λ/2 plate can be changed between 267 nm and 317 nm;

FIG. 39B is a characteristic diagram showing azimuth dependence ofreflectance (for a directional reflector) of a polarizing plate+abroadband λ/4 plate+a liquid crystal layer when the in-plane retardationof a λ/2 plate can be changed between 267 nm and 317 nm;

FIG. 40 is a characteristic diagram showing, on a directional reflector,azimuth dependence of the reflectance of a polarizing plate+a broadbandλ/4 plate+a liquid crystal layer when the in-plane retardations of botha λ/4 plate and a λ/2 plate can be changed;

FIG. 41 is a characteristic diagram showing azimuth dependence of thereflectance of a polarizing plate for every polar angle;

FIG. 42A is a characteristic diagram showing azimuth dependence of thereflectance (for a non-directional reflector) of a polarizing plate+abroadband λ/4 plate+an optical compensation plate+a liquid crystal layerwhen the in-plane retardation of a λ/4 plate can be changed between 128nm and 159 nm;

FIG. 42B is a characteristic diagram showing azimuth dependence of thereflectance (for a directional reflector) of a polarizing plate+abroadband λ/4 plate+an optical compensation plate+a liquid crystal layerwhen the in-plane retardation of a λ/4 plate can be changed between 128nm and 159 nm;

FIG. 43A is a characteristic diagram showing azimuth dependence of thereflectance (for a non-directional reflector) of a polarizing plate+abroadband λ/4 plate+an optical compensation plate+a liquid crystal layerwhen the in-plane retardation of a λ/2 plate can be changed between 240nm and 285 nm;

FIG. 43B is a characteristic diagram showing azimuth dependence of thereflectance (for a directional reflector) of a polarizing plate+abroadband λ/4 plate+an optical compensation plate+a liquid crystal layerwhen the in-plane retardation of a λ/2 plate can be changed between 240nm and 285 nm;

FIG. 44 is a characteristic diagram showing, on a directional reflector,azimuth dependence of the reflectance of a polarizing plate+a broadbandλ/4 plate+an optical compensation plate+a liquid crystal layer when thein-plane retardations of both a λ/4 plate and a λ/2 plate can bechanged; and

FIG. 45A and FIG. 45B are perspective views showing optical compensationplate configurations of conventional reflection-type liquid crystaldisplay devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

—Main points of the Present Invention—

(Main Point 1)

To solve the above-described problems, the present invention aims toreduce the number of films while using general-purpose films, and tooptimize the retardation of a liquid crystal panel in conformitythereto. Specifically, at least two retardation plates are used tocreate, in a combined manner, the function of a λ/4 plate and thefunction of a negative retardation plate. The λ/4 plate here is a filmhaving a retardation of a quarter of the wavelength of assumed light,for example, visible light. Besides, the negative retardation Rm isdefined by Rm=((n_(x)+n_(y))/2−n_(z))·d where the refractive indexes inan x direction, a y direction and a z direction are n_(x), n_(y), andn_(z) respectively, and the optical path length is d.

[Principle Configuration 1]

A specific principle configuration of the present invention is shown inFIG. 1.

A main configuration of a liquid crystal display device of the presentinvention is made by providing, for example, a liquid crystal layer inwhich vertically aligned liquid crystal molecules tilt in a 0° azimuthwhere voltage is applied, a λ/4 plate 1 being a first retardation plate,for example, a λ/2 plate 2 being a second retardation plate, and apolarizing plate 3, in this order from the side of a liquid crystalpanel (only a reflecting electrode, a liquid crystal layer, and atransparent electrode are shown representing a liquid crystal panel forconvenience in FIG. 1 and later-described FIG. 2 and FIG. 3). In thisconfiguration, an angle formed between an absorption axis of thepolarizing plate 3 and an absorption axis of the λ/2 plate 2 is about45°, an in-plane retardation of the λ/2 plate 2 is set to a valueobtained by adding λ/4 to an in-plane retardation of the retardationplate 1, desirably, the λ/4 plate 1 (For example, when the in-planeretardation of the retardation plate 1, desirably, the λ/4 plate 1 isλ/4+α, the in-plane retardation of the λ/2 plate 2 is λ/2+α. Theretardation plate 1 is described as the λ/4 plate 1 hereinafter, but isnot limited to the λ/4 plate.), and an optical axis of the λ/4 plate 1and an optical axis of the λ/2 plate 2 are orthogonal to each other. Inthis configuration, the optical axis of the λ/4 plate 1 is placed at150°, the optical axis of the λ/2 plate 2 is placed at 60°, and theabsorption axis of the polarizing plate 3 is placed at 15°.

Note that the liquid crystal panel is shown in the form in which theliquid crystal layer is sandwiched between a lower substrate with areflecting layer formed thereon and an upper substrate with atransparent electrode formed thereon, for convenience in the exampleshown in the drawing.

The λ/2 plate 2 practically has a function obtained by superposing tworetardation plates, that is, λ/4 plates 2 a and 2 b having optical axesboth at angles of 60°. The retardation of plate 2 is obtained by addingλ/4 to the retardation of plate 2 a. Further, the optical axes of theλ/4 plate 2 a and λ/4 plate 1 are orthogonal to each other so that theirin-plane retardations cancel each other out to be 0, and only the sum ofnegative retardations of them remains. In other words, the superpositionof the λ/4 plate 1 and the λ/2 plate 2 provides the same function asthat of a configuration provided with a negative retardation plate 4 anda λ/4 plate 5 as shown in FIG. 2A. In FIG. 2A, the vertically alignedliquid crystal molecule tilts in a 0° azimuth where voltage is applied.

Although the case in which each of the λ/4 plate 2 a and the λ/4 plate 1has an in-plane retardation of λ/4 is taken as an example here, thevalue of the negative retardation is determined by the relation betweenrefractive indexes of the λ/4 plate here. For a completely uniaxialretardation plate, the negative retardation is 137 nm because n_(y) andn_(z) are equal. However, it is typical that a biaxial λ/4 plate isproduced depending on the manufacturing method, and therefore the abovevalue slightly varies. Here, especially when n_(z) is greater thann_(y), the viewing angle characteristics are better.

[Principle Configuration 2]

A specific principle configuration is shown in FIG. 3 as another exampleof the present invention. Only a reflecting electrode, a liquid crystallayer, and a transparent electrode are representatively illustrated herefor convenience.

A main configuration of a liquid crystal display device of the presentinvention is made by providing, for example, a λ/4 plate 11 being afirst retardation plate, for example, a λ/2 plate 12 being a secondretardation plate, a λ/2 plate 13 being a third retardation plate, and apolarizing plate 14, in this order from the side of a liquid crystalpanel. It should be noted that the λ/2 plate 12 and the λ/2 plate 13 maybe described together as the second retardation plate. In thisconfiguration, where the angle formed between an absorption axis of thepolarizing plate 14 and an optical axis of the λ/2 plate 13 is θ, anangle formed between the optical axis of the λ/2 plate 13 and an opticalaxis of the λ/2 plate 12 is θ±45°, an in-plane retardation of the λ/2plate 12 should be a value obtained by adding λ/4 to an in-planeretardation of the λ/4 plate 11 (For example, when the in-planeretardation of the λ/4 plate 11 is λ/4+β, the in-plane retardation ofthe λ/2 plate 12 is λ/2+β.), and an optical axis of the λ/4 plate 11 andthe optical axis of the λ/2 plate 12 are orthogonal to each other. Here,the optical axis of the λ/4 plate 11 is placed at 170°, the optical axisof the λ/2 plate 12 is placed at 80°, the optical axis of the λ/2 plate13 is placed at 25°, and the absorption axis of the polarizing plate 14is placed at 15°.

The λ/2 plate 12 practically has a function obtained by superposing tworetardation plates, that is, λ/4 plates 12 a and 12 b having opticalaxes both at angles of 80°. The in-plane retardation of the λ/2 plate 12is the sum of an in-plane retardation of the λ/4 plate 12 a and λ/4, andthe in-plane retardation of the λ/4 plate 12 a is the same as thein-plane retardation of the λ/4 plate 11. In this case, thesuperposition of the λ/4 plate 12 b and the λ/2 plate 13 creates afunction of the λ/4 plate of reverse dispersion. Further, the opticalaxes of the λ/4 plate 12 a and λ/4 plate 11 are orthogonal to each otherso that their in-plane retardations cancel each other out to be 0, andonly the sum of negative retardations of them remains. In other words,the superposition of the λ/4 plate 11 and the λ/2 plate 12 provides thesame function as that of a configuration provided with a negativeretardation plate 15 and a λ/4 plate 16 as shown in FIG. 2B. In FIG. 2B,the vertically aligned liquid crystal molecule tilts in a 0° azimuthwhere voltage is applied.

The value of the negative retardation is determined by the relationbetween refractive indexes of the retardation plate here. For acompletely uniaxial retardation plate, the negative retardation is halfthe in-plane retardations of the retardation plate because n_(y) andn_(z) are equal. In this example, the negative retardation is the sameas the in-plane retardations because of a combination of the tworetardation plates. However, it is typical that a biaxial plate isproduced depending on the manufacturing method, and therefore the abovevalue slightly varies. Here, especially when n_(z) is greater thann_(y), the viewing angle characteristics are better.

(Main point 2)

In the present invention, the vertical alignment (VA) mode using onepolarizing plate is used as the display mode, in which a retardationplate having a specific retardation for every average tilt angle ofreflecting projections and depressions is arranged between thepolarizing plate and a liquid crystal layer. This can propose optimalcompensation conditions for every average tilt angle and realizecompensation using a less expensive retardation plate. The large andsmall average tilt angles are selectively used in such a manner that asmall average tilt angle is used for a small panel and a large averagetilt angle is used for a large panel. This is because it is assumed thatthe small panel is used in an environment closer to a light sourcebecause of its good portability, in which case light emitted in avertical direction to the substrate is incident at a relatively shallowangle. On the other hand, it is assumed that the large panel is used inan environment rather far from a light source, such as on a desk or thelike, because of its poor portability, in which case light emitted in avertical direction to the substrate is incident at a relatively deepangle.

The VA mode is reverse to the TN mode in the switching, but is the samein performance of black display by converting incident environmentallight into linearly polarized light by a polarizing plate, and rotatingits polarization azimuth 90° by a retardation plate having a retardationof about a quarter of the visible light wavelength so as to cause apolarizing plate to absorb it. In the VA mode, however, since the blackdisplay is performed where no voltage is applied, it never happens thata liquid crystal layer anchoring to the interface of the substrateremains without switching as in the TN mode, resulting in improvedcontrast ratio in principle.

However, in the reflection-type liquid crystal display device with thereflecting projections and depressions, since light reflected to theobserver side (in a substrate vertical direction) is an almost obliqueincidence, and the liquid crystal on the substrate interface is alsotilt-aligned due to the reflecting projections and depressions, theliquid crystal layer has a retardation even where no voltage is applied.It is possible to estimate this retardation since the incident andemitted angles of light with respect to the liquid crystal can beobtained if the observation angle (emitted angle) to the substratesurface and the tilt angle distribution of the reflecting projectionsand depressions are already known, and it is possible to obtaincompletely black display by canceling the retardation of a liquidcrystal layer through use of a retardation plate having a negativerefractive index anisotropy in a substrate vertical direction and havinga retardation substantially equivalent to this retardation.

As the technique for compensating the retardation of a verticallyaligned liquid crystal layer through use of the retardation plate havinga negative refractive index anisotropy in the substrate verticaldirection, there is a known method in which elliptically polarized lightis generated from obliquely incident light, the long axis of theelliptically polarized light forming a fixed angle with respect to anobservation surface, and a retardation plate is configured to erase thisangle when the obliquely falling light has completely passed through theliquid crystal layer (see Patent Document 4). This technique ischaracterized in that the retardation plate is set so that the obliquelyincident light becomes circularly polarized light when reaching areflector.

However, in the reflection-type liquid crystal display device having thereflecting projections and depressions, since the liquid crystal istilt-aligned due to the reflecting projections and depressions, theincident angle of light to the liquid crystal in an approach routediffers from that in a return route, and retardations occurring thereinare also different from each other. In the aforementioned technique,when the retardations occurring in the approach route and return routeare equal, they are established as compensation conditions, but when theretardations are different from each other, they are not established ascompensation conditions because of generation of discrepancytherebetween.

Further, there is another known method for performing compensationthrough use of a birefringence compensation medium (retardation plate)with one refractive index (n_(z)) lower than two other refractiveindexes (n_(x), n_(y)) (see Patent Document 5). This techniquecompensates the retardation which occurs when the liquid crystal displaydevice is viewed from an oblique direction, through use of a retardationplate having a refractive index anisotropy of n_(x), n_(y)>n_(z), butsuch a retardation plate needs to be subjected to advanced stretchingprocessing such as biaxial stretching in order to prevent occurrence ofa large retardation in the substrate in-plane direction and is thusexpensive as compared to a uniaxially stretched retardation plate.

[Principle Configuration 1]

This liquid crystal display device comprises a reflecting layer forreflecting incident light, a liquid crystal layer provided on thereflecting layer, in which alignment of liquid crystal molecules isvertical, and a retardation plate and a polarizing plate which areprovided on a front surface of the liquid crystal layer. The reflectinglayer has projections and depressions formed on a surface thereof, anaverage tilt angle of the projections and depressions being a value ofnot less than about 4° nor greater than about 6°, and the retardationplate has a negative refractive index anisotropy in a vertical directionto a surface thereof, a ratio between a retardation Rf thereof and aretardation Rlc of the liquid crystal layer, Rf/Rlc, being a value ofnot less than 0.6 nor greater than 0.9. It is possible to estimate theretardation of the liquid crystal layer where no voltage is applied fromthe observation angle (emitted angle) to the substrate surface and thetilt angle distribution of reflecting projections and depressions, butsuch a problem often happens that an optimal retardation at anobservation angle is not optimal at another observation angle. Thisdifference is conspicuous especially when the average tilt angle of thereflecting projections and depressions is small, and therefore lightgreatly leaks at a specific angle, leading to great loss of contrastcharacteristics, unless a retardation plate is selected in fullconsideration of at which observation angle the retardation is to becancelled prior to others.

Specifically, when the average tilt angle of the reflecting projectionsand depressions is not less than about 4° nor greater than about 6°,light emitted at an observation angle of 0° (in the substrate verticaldirection) is incident on/emitted from the liquid crystal layer at ashallow angle of not less than about 0° nor greater than about 12°, sothat the optimal retardation is small, while light emitted at anobservation angle of 45° is incident on/emitted from the liquid crystallayer at a deep angle of not less than about 16° nor greater than about28°, so that the optimal retardation is large. When the optimalretardation greatly differs depending on the observation angle asdescribed above, it is preferable to set a retardation plate inconformity to the larger retardation. This leads to excessivecompensation at the observation angle of 0° to cause black floating, butthe light emitted at the observation angle of 0° is incident on theliquid crystal layer at a shallow angle, so that the retardation due tothe excessive compensation is also small, resulting in little influence.In this way, finding the optimal retardation Rf from the observationangle which causes a large retardation and the average tilt angle of thereflecting projections and depressions results in substantially0.6≦Rf/Rlc≦0.9. The reason why the tilt angle of the reflectingprojections and depressions is shown not by the tilt angle distributionbut by the average tilt angle is that the average tilt angle is thecenter of probability which can be obtained from the tilt angledistribution, and therefore the central value causes only a small erroreven if it is used for discussion of the tilt angle.

Besides, the reason why Rf is expressed through the ratio with respectto the retardation Rlc which is obtained from the cell thickness and thebirefringence difference of the liquid crystal layer is that Rf of theretardation plate changes in proportion to the retardation Rlc of theliquid crystal layer. The reason why the observation angles are set to0° and 45° is that about 0° is for the case in which an observer holdsthe reflection-type liquid crystal display device in hands and observesit in front of him or her, and about 45° is for the case in which theobserver puts the reflection-type liquid crystal display device on adesk or the like and observes it in an oblique direction, and thereforeif these two different observation angles are taken into considerationto estimate the optimal retardation, substantially excellent contrastcharacteristics can be expected within a practical observation range. Onthe contrary, an observation angle greater than this, even when regardedas one to be compensated, exceeds a practically required observationrange and also undesirably causes a great trade off with front surfacecharacteristics.

[Principle Configuration 2]

This liquid crystal display device comprises a reflecting layer forreflecting incident light, a liquid crystal layer provided on thereflecting layer, in which alignment of liquid crystal molecules isvertical, and a retardation plate and a polarizing plate provided on afront surface of the liquid crystal layer. The reflecting layer hasprojections and depressions formed on a surface thereof, an average tiltangle of the projections and depressions being a value of not less thanabout 7° nor greater than about 9°, and the retardation plate has anegative refractive index anisotropy in a vertical direction to asurface thereof, a ratio between a retardation Rf thereof and aretardation Rlc of the liquid crystal layer, Rf/Rlc, being a value ofnot less than 0.5 nor greater than 0.8. When the average tilt angle ofthe reflecting projections and depressions is not less than about 7° norgreater than about 9°, light emitted at an observation angle of 0° (inthe substrate vertical direction) is incident on/emitted from the liquidcrystal layer at not less than about 0° nor greater than about 18°,while light emitted at an observation angle of 45° is incidenton/emitted from the liquid crystal layer at an angle of not less thanabout 10° nor greater than about 28°. When the average tilt angle isincreased, incident angles on the liquid crystal partially overlap witheach other, so that the difference in retardation depending on theobservation angle decreases. Accordingly, finding the optimalretardation Rf results in substantially 0.5≦Rf/Rlc≦0.8.

[Principle Configuration 3]

This liquid crystal display device comprises a reflecting layer forreflecting incident light, a liquid crystal layer provided on thereflecting layer, in which alignment of liquid crystal molecules isvertical, and a retardation plate and a polarizing plate provided on afront surface of the liquid crystal layer. The reflecting layer hasprojections and depressions formed on a surface thereof, an average tiltangle of the projections and depressions being a value of not less thanabout 10° nor greater than about 15°, and the retardation plate has anegative refractive index anisotropy in a vertical direction to asurface thereof, a ratio between a retardation Rf thereof and aretardation Rlc of the liquid crystal layer, Rf/Rlc, being a value ofnot less than 0.4 nor greater than 0.7. When the average tilt angle ofthe reflecting projections and depressions is not less than about 10°nor greater than about 15°, light emitted at an observation angle of 0°(in the substrate vertical direction) is incident on the liquid crystallayer at about 10° to about 30°, while light emitted at an observationangle of 45° is incident on the liquid crystal layer at an angle of notless than about 0° nor greater than about 28°. When the average tiltangle is further increased, incident angles on the liquid crystalsubstantially overlap with each other, so that retardations at theobservation angles decrease in difference of magnitude or becomesubstantially equal. In such a case, it is only required to performarbitrary selection depending on at which observation angle the contrastratio is given priority, and finding the optimal retardation Rf resultsin substantially 0.4≦Rf/Rlc≦0.7.

In the principle configurations 1 to 3, the retardation plate preferablyhas an N_(z) coefficient of 1 or less. The N_(z) coefficient isexpressed by N_(z)=(n_(x)−n_(z))/(n_(x)−n_(y)), so that for the N_(z)coefficient to be 1 or less, (n_(x)−n_(z)) needs to be smaller than(n_(x)−n_(y)), that is, n_(y)≦n_(z). The retardation plate with n_(x),n_(y)>n_(z) needs to have the refractive index anisotropy in thesubstrate in-plane direction less than that in the substrate verticaldirection and is therefore produced by an advanced technique such asbiaxial stretching, but the retardation plate with n_(y)≦n_(z) may havea large refractive index anisotropy in the substrate in-plane directionand can therefore be produced by a simple technique such as uniaxialstretching. However, the VA mode requires extra compensation films ascompared to the TN mode, and therefore the cost of the compensation filmneeds to be minimized.

In the principle configurations 1 to 3, it is preferable that theretardation plate is constituted of a plurality of uniaxially stretchedfilms and arranged in layers such that the respective slow axes aresubstantially orthogonal to each other. The retardation plates producedby uniaxial stretching have retardations in the substrate in-planedirection, so that arrangement of them in layers such that therespective slow axes are substantially orthogonal to each other allowsthe retardations in the substrate in-plane direction to cancel eachother and only the retardations in the substrate vertical direction toremain. Although there is no problem to use a single uniaxiallystretched retardation plate, the uniaxially stretched retardation platehas a small retardation as compared to a biaxially stretched retardationplate to fail to perform sufficient compensation. The arrangement ofuniaxially stretched retardation plates in layers such that therespective slow axes are substantially orthogonal to each other allowsarbitrary setting of the retardations in the substrate verticaldirection.

(Main Point 3)

The plane shapes of reflecting projections and depressions are changedfrom dot forms into geometrical forms in which reflecting surfaces areoriented toward a specific azimuth, and the forms are arbitrarilycontrolled, thereby making it possible to efficiently reflecting lightincident from the specific azimuth to the observer side.

The present inventor proposes a technique for forming geometricalreflecting projections and depressions without pattern formation byusing the difference in hardening shrinkage of a photosensitive resin.Besides, the display mode is changed from the TN mode to the verticalalignment (VA) mode in which liquid crystal having a negative dielectricconstant anisotropy is vertically aligned, thereby eliminating liquidcrystal anchoring to the substrate interface, so that the contrast ratiocan be increased in principle. Efficient reflection of light incidentfrom the specific azimuth to the observer side and use of the VA mode asthe display mode can realize display that is easy to view even in aninterior environment.

However, since the azimuthal anisotropy of the reflection intensitydiffers even depending on panel parameters such as the axis placement ofthe polarizing plate and the alignment azimuth of liquid crystal, thecontrast ratio is reduced in an azimuth in which the reflectionintensity is maximum when the parameters do not match the reflectioncharacteristics created by the reflecting projections and depressions,resulting in display with poor visibility. Hence, the present inventordiscovered that the technique shown below enables matching of thereflecting projections and depressions with the panel parameters tomaximize the contrast ratio in the azimuth in which the reflectionintensity is maximum due to the reflecting projections and depressions,thereby enabling the display to be easy to view.

[Principle Configuration 1]

This liquid crystal display device comprises a reflecting layer withprojections and depressions having azimuthal anisotropies on reflectionintensity formed on a surface thereof, for reflecting incident light, aliquid crystal layer provided on the reflecting layer, in whichalignment of liquid crystal molecules is vertical, and a retardationplate and a polarizing plate provided on a front surface of the liquidcrystal layer. The retardation plate has a retardation of a quarter of avisible light wavelength in an in-plane direction thereof, and isarranged such that an angle formed between an azimuth φ in which thereflection intensity is maximum and an absorption axis P of thepolarizing plate is a value of not less than about 65° nor greater thanabout 90°, and an angle formed between a slow axis F₁ of the retardationplate and the absorption axis P is about 45°. The azimuthal anisotropyof the reflection intensity due to the axis placement of the polarizingplate is such that, in the case of a single polarizing plate, thereflection intensity is maximum in an azimuth of its transmission axisand the reflection intensity is minimum in an azimuth of the absorptionaxis, due to absorption characteristics of the polarizing plate. Whenthe retardation plate having a retardation of about a quarter of thevisible light wavelength is added to the above arrangement, thepolarization azimuth is rotated, so that the reflection intensity isminimum in the azimuth of the transmission axis and the azimuth of theabsorption axis.

More specifically, when light goes and returns through the retardationplate having a retardation of about a quarter of the visible lightwavelength, the polarization azimuth is rotated 90° with the slow axisof the retardation plate as a symmetrical axis, but if arrangement ismade such that the angle formed between the slow axis of the retardationplate and the absorption axis of the polarizing plate is about 45°,linearly polarized light in the azimuth of the transmission axis isrotated 90° to be parallel to the absorption axis of the polarizingplate, resulting in a minimum reflection intensity. In an azimuth otherthan 45°, however, the polarization azimuth is rotated to deviate fromthe absorption axis of the polarizing plate, causing leakage of light.Further, when a liquid crystal layer having a retardation of about aquarter of the visible light wavelength is added to the abovearrangement, the polarization azimuth is rotated 180° to be parallel tothe transmission axis of the polarizing plate, resulting in a maximumreflection intensity in the azimuth of the transmission axis as in thecase of only the polarizing plate. Accordingly, if the polarizing plateand the retardation plate are arranged such that the angle formedbetween the azimuth φ in which the reflection intensity is maximum dueto the reflecting projections and depressions and the absorption axis Pof the polarizing plate is about 90°, and the angle formed between theslow axis F₁ of the retardation plate and P is about 45°, the contrastratio will be maximum in the azimuth in which the reflection intensityis maximum due to the reflecting projections and depressions.

However, since obliquely incident light is mainly reflected to theobserver side (in the substrate vertical direction) by thereflection-type liquid crystal display device having reflectingprojections and depressions, the oblique incidence causes retardation todeviate the polarization azimuth, and the polarization azimuth deviatesfrom the absorption axis of the polarizing plate also in the azimuth ofthe transmission axis, resulting in leakage of light (correctly,elliptically polarized light with polarization azimuth deviated). Forcorrection of this, it is effective to rotate in a reverse direction theaxis placement of the polarizing plate by the amount of deviation of thepolarization azimuth to thereby give it offset, whereby the polarizationazimuth becomes substantially parallel to the absorption axis of thepolarizing plate.

Here, the retardation plate is configured having a first retardationplate having a retardation of a half of a visible light wavelength in anin-plane direction thereof and a second retardation plate having aretardation of a quarter of a visible light wavelength in an in-planedirection thereof, in which it is preferable that an angle formedbetween a slow axis F₁₁ of the first retardation plate and an absorptionaxis P is not less than about 0° nor greater than about 20°, and anangle formed between a slow axis F₁₂ of the second retardation plate andthe slow axis F₁₁ is not less than about 45° nor greater than about 65°.The retardation plate is generally produced by stretching norbornenepolymer films, but the polymer film has wavelength dispersion, andtherefore if the retardation plate is designed to have a retardation ofabout a quarter of a specific wavelength, the retardation for otherwavelengths deviates from about a quarter thereof. To relax thewavelength dispersion of the retardation plate so that the retardationplate has a retardation of about a quarter of almost all of thewavelengths of visible light, there is a method of using a materialhaving wavelength dispersion less than that of norbornene films or oflayering retardation plates such as to decrease the wavelengthdispersion. As for the former, the material is more expensive thannorbornene films, and as for the latter, a structure in which aretardation plate having a retardation of about a half of the visiblelight wavelength and a retardation plate having a retardation of about aquarter of the visible light wavelength are layered, is typical and inwide use as a broadband λ/4 plate (or a λ/4 plate). The broadband λ/4plate is preferably arranged such that an angle formed between a slowaxis of the broadband λ/4 plate and the absorption axis of thepolarizing plate is also about 45° or 135°, and since the slow axis ofthe broadband λ/4 plate corresponds to a vector made by combining theslow axis of the first retardation plate and the slow axis of the secondretardation plate, the respective retardation plates are preferablyarranged such that the combined vector is substantially equivalent tothe above-described slow axes of the retardation plates.

[Principle Configuration 2]

This liquid crystal display device comprises a reflecting layer withprojections and depressions having azimuthal anisotropies on reflectionintensity formed on a surface thereof, for reflecting incident light, aliquid crystal layer provided on the reflecting layer, and provided onthe reflecting layer, and a retardation plate and a polarizing plateprovided on a front surface of the liquid crystal layer. The retardationplate has a retardation of a quarter of a visible light wavelength in anin-plane direction thereof, and is arranged such that an angle formedbetween an azimuth φ in which the reflection intensity is maximum and anabsorption axis P of the polarizing plate is a value of not less thanabout 90° nor greater than about 115°, and an angle formed between aslow axis F₁ of the retardation plate and the absorption axis P is about135°. Even when the arrangement is made such that the angle formedbetween the slow axis of the retardation plate and the absorption axisof the polarizing plate is about 135°, the polarization azimuth oflinearly polarized light incident from the azimuth of the transmissionaxis similarly deviates, the deviation being in the opposite directionto the case of 45°. Therefore, to correct the deviation of thepolarization azimuth, it is preferable to rotate the axis placement ofthe polarizing plate in the opposite direction to the case of 45°.

Here, it is preferable that the retardation plate is configured having afirst retardation plate having a retardation of a half of a visiblelight wavelength in an in-plane direction thereof and a secondretardation plate having a retardation of a quarter of a visible lightwavelength in an in-plane direction thereof, and an angle formed betweena slow axis F₁₁ of the first retardation plate and the absorption axis Pis not less than about 0° nor greater than about 20°, and an angleformed between a slow axis F₁₂ of the second retardation plate and theslow axis F₁₁ is not less than about 135° nor greater than about 155°.Since a slow axis of a broadband λ/4 plate corresponds to a vector madeby combining the slow axis of the first retardation plate and the slowaxis of the second retardation plate, the respective retardation platesare preferably arranged such that the combined vector is substantiallyequivalent to the above-described slow axes of the retardation plates.

Here, in the principle configurations 1 and 2, it is preferable thatthere is another retardation plate having retardations in a verticaldirection to a surface thereof and an in-plane direction thereofrespectively, and the other retardation plate is arranged on the liquidcrystal layer side of the retardation plate such that an angle formedbetween an azimuth φ in which the reflection intensity is maximum and aslow axis F₂ of at least one of the retardation plate and the otherretardation plate is not less than about 0° nor greater than about 30°.The deviation of the polarization azimuth due to an oblique incidentoccurs not only in the retardation plate but also in the liquid crystallayer. The retardation of the liquid crystal layer varies depending onthe voltage, in which application of voltage causes the retardation ofthe liquid crystal layer to be about a quarter of the visible lightwavelength, leading to white display in the VA mode. The deviation ofthe polarization azimuth is not so problematic in the white displaybecause the rate of change in reflection intensity is low, while therate is high in black display, that is, in a state in which no voltageis applied to the liquid crystal layer, leading to a great decrease inthe contrast ratio. Although the deviation of the polarization azimuthin the retardation plate results from deviation from the retardation ofabout a quarter of the visible light wavelength caused by a negativeretardation occurring due to an oblique incidence, the deviation of thepolarization azimuth in the liquid crystal layer in the state where novoltage is applied, namely, which is vertically aligned results from newoccurrence of a positive retardation due to the oblique incidence.Accordingly, to correct the deviation of the polarization azimuth in theliquid crystal layer due to the oblique incidence, it is necessary tocancel the positive retardation by the negative retardation, andtherefore proposed is means for canceling the retardation of the liquidcrystal layer through use of a retardation plate having a negativeretardation in the substrate vertical direction (see Patent Documents 6and 7). The refractive index anisotropy of the vertically aligned liquidcrystal layer is in a substantially ellipsoid which is longer than iswide, and therefore by using a retardation plate having a refractiveindex anisotropy opposite thereto, that is, a retardation plate having anegative retardation in the substrate vertical direction, the respectiverefractive index anisotropies cancel each other out, so that retardationdue to the oblique incidence no longer occurs.

To give such a retardation to a retardation plate made of a polymerfilm, advanced stretching processing such as biaxial stretching isrequired to prevent occurrence of excessive retardation in the substratein-plane direction, leading to a rise in price. However, a retardationplate uniaxially stretched for the purpose of giving a retardation inthe substrate in-plane direction also has a negative retardation in thesubstrate vertical direction, and therefore such retardation plates arelayered such that slow axes thereof are orthogonal to each other,whereby only the retardation of the vertically aligned liquid crystallayer can be canceled without occurrence of excessive retardation in thesubstrate in-plane direction. For example, a retardation plate having aretardation of about a quarter of the visible light wavelength in thesubstrate in-plane direction also has a negative retardation from about1/10 to ⅙ the visible light wavelength in the substrate verticaldirection, and therefore such retardation plates are layered such thatslow axes thereof are orthogonal to each other, whereby the retardationof the liquid crystal layer can be canceled through use of inexpensiveretardation plates.

However, in the structure in which the uniaxially stretched retardationplates are layered such that the slow axes thereof are orthogonal toeach other, deviation occurs in the polarization azimuth because the twoslow axes exhibit different behaviors at the time of tilt in an azimuthdifferent from the slow axes. More specifically, the refractive indexanisotropy for an oblique incidence corresponds to the shape of a crosssection made by cutting an ellipsoid at an incidence surface, and whenapparent slow axes change due to exhibition of the different behaviorsof the two slow axes, the shapes of the cross sections also change tocause deviation between retardations, leading to occurrence of deviationin polarization azimuth. Accordingly, the retardation plates arearranged in layers such that the angle formed between the azimuth inwhich the reflection intensity is maximum and the slow axis of at leastone of the retardation plates is not less than about 0° nor greater thanabout 30°, thereby eliminating the exhibition of different behaviors ofthe two slow axes at the time of tilt in the azimuth in which thereflection intensity is maximum to enable effective cancellation of theretardation of the liquid crystal layer caused by the oblique incidencein the azimuth in which the reflection intensity is maximum due to thereflecting projections and depressions.

[Principle Configuration 3]

This liquid crystal display device comprises a reflecting layer withprojections and depressions having azimuthal anisotropies on reflectionintensity formed on a surface thereof, for reflecting incident light,and a liquid crystal layer provided on the reflecting layer, in whichliquid crystal molecules of the liquid crystal layer are aligned suchthat an angle formed between an azimuth φ in which the reflectionintensity is maximum and a director azimuth L for the liquid crystalmolecules is not less than about 45° nor greater than about 90°. Whenthe plane shapes of the reflecting projections and depressions are ingeometrical forms in which tilt surfaces are oriented toward the azimuthin which the reflection intensity is high, the liquid crystal moleculeson the substrate interface initially tilt in the azimuth in which thereflection intensity is high. Further, the liquid crystal on thesubstrate interface initially tilts even by alignment control such asrubbing processing. When the liquid crystal molecules initially tilt,the reflection intensity increases in black display to decrease thecontrast ratio, but when the angle formed between the azimuth in whichthe liquid crystal initially tilts due to the reflecting projections anddepressions and the azimuth in which the liquid crystal initially tiltsby the alignment control differ from each other within a range not lessthan about 45° nor greater than about 90°, preferably at about 90°, theretardation of the initially tilted liquid crystal is canceled so thatthe contrast ratio can be improved.

Here, it is preferable to use the reflecting projections and depressionshaving azimuthal anisotropies on reflection intensity so as to align theliquid crystal in the applicable azimuth. Since the reflectingprojections and depressions function as conductive protrusions, theliquid crystal near the reflecting projections and depressions isaligned in the azimuth substantially parallel to the tilt surfaces. Thisis because when the azimuth in which the liquid crystal initially tiltsdiffers from the azimuth in which the liquid crystal is tilt-aligned dueto an oblique electric field, the liquid crystal on the tilt surfacesbecomes hard to be aligned in the tilt azimuth, and as a result, theliquid crystal near the reflecting projections and depressions is drawnin the alignment azimuth on the protrusions and aligned in the azimuthsubstantially parallel to the tilt surfaces. Hence, the reflectingprojections and depressions are densely arranged such that the tiltsurfaces of the reflecting projections and depressions are substantiallyparallel to the azimuth in which the reflection intensity is maximum,whereby the reflecting projections and depressions can align the liquidcrystal in the applicable azimuth. The tilt angle of the liquid crystalby the alignment control through use of the reflecting projections anddepressions is not too large, unlike that by the rubbing processing, sothat the contrast ratio is not reduced even with alignment control meansprovided on upper and lower substrates, and the alignment stability alsoimproves.

Besides, it is preferable to use slits formed on pixel electrodes so asto align the liquid crystal in the applicable azimuth. Since the slitsfunction as an insulator, the liquid crystal near the slits is alignedin an azimuth substantially parallel to long sides of the slits wherevoltage is applied, if the width of the slit is made small to a degreeat which the region where the oblique electrical field occurs isdecreased. This is because the liquid crystal molecules at slit edgeportions become hard to be tilt-aligned in the azimuth of the obliqueelectric field because the region where the oblique electric fieldoccurs is decreased, and as a result, the liquid crystal molecules nearthe slits are drawn in the alignment azimuth on the slits and alignedsubstantially parallel to the long sides of the slits. Hence, the slitsare arranged such that the long sides of the slits are substantiallyparallel to the azimuth in which the reflection intensity is maximum,whereby the slits can align the liquid crystal in the applicableazimuth. The alignment control through use of the slits can realize atransflective-type liquid crystal display device by making the portionsabove the slits transmission regions, in addition to the alignmentstability.

(Main point 4)

Here, in the configuration of the main point 3 in the VA mode(configuration with reflecting projections and depressions havingazimuthal anisotropies on reflection intensity), the azimuth dependenceof the retardation in a direction of the thickness of the liquid crystaldisplay device is controlled to increase the contrast ratio in theazimuth in which the reflection intensity is maximum.

[Principle Configuration 1]

In this liquid crystal display device, as shown in FIG. 4, a lower glasssubstrate 31 and an upper glass substrate 32 hold a liquid crystal layer33, which is composed of liquid crystal molecules with negativedielectric constant anisotropies, sandwiched therebetween, a wrinkledreflecting electrode 34 with projections and depressions havingazimuthal anisotropies on reflection intensity formed on the surface isprovided between the lower glass substrate 31 and the liquid crystallayer 33, and a transparent electrode 35 is provided between the upperglass substrate 32 and the liquid crystal layer 33 respectively.Further, a λ/4 plate 36, a λ/2 plate 37, and a polarizing plate 38 areprovided on (a front surface of) the upper glass substrate 32, andconfigured such that the λ/4 plate 36 and λ/2 plate 37 are different inapplicable wavelength, and the retardations caused by the λ/4 plate 36,the λ/2 plate 37, and the liquid crystal layer 33 due to an obliqueincidence or oblique emission in an azimuth in which the reflectionintensity is maximum are smaller than the retardations in an azimuth inwhich the reflection intensity is minimum.

The combination of the λ/4 plate and λ/2 plate is in wide use as abroadband λ/4 plate, and the broadband λ/4 plate also has a negativeretardation in the thickness direction like an optical compensationplate. Their applicable wavelengths are made different from 550 nm thatis a visibility peak wavelength, that is, the in-plane retardations aredeviated from 137.5 nm in the λ/4 plate and 275 nm in the λ/2 plate tothereby control the azimuth dependency of the retardation in thethickness direction so that the retardation caused by the liquid crystallayer 33, the λ/4 plate 36, and the λ/2 plate 37 due to an obliqueincidence or oblique emission in the azimuth in which the reflectionintensity is maximum is smaller than that in the azimuth in which thereflection intensity is low, whereby the contrast ratio can beincreased. Although the contrast ratio is decreased in the azimuth inwhich the reflection intensity is low because the retardation in thethickness direction shifts in the opposite direction, leakage of lightcan be reduced to a low degree at which no problem is caused in terms ofdisplay by application of the reflecting projections and depressionshaving azimuthal anisotropies on the reflection intensity like thewrinkled reflecting electrode 34.

In this point, a technique is proposed also in the prior art forimproving the contrast ratio by reducing the retardation of the λ/4plate, that is, decreasing the applicable wavelength, but the prior artis for compensating the retardation of the liquid crystal layeranchoring to the substrate interface where voltage is applied, and isthus different from the present invention in that the slow axis of theλ/4 plate is made substantially coincident with the anchoring(alignment) azimuth of the liquid crystal layer, and the applicablewavelength is adjusted so that the sum of the in-plane retardation ofthe liquid crystal layer and the in-plane retardation of the λ/4 plateis about 137.5 nm.

The present invention is for compensating the retardation of the liquidcrystal layer caused by an oblique incidence where no voltage isapplied, in which each of applicable wavelengths of the λ/4 plate andthe λ/2 plate is adjusted so that the difference between the retardationoccurring in the liquid crystal layer and the retardation occurring inan optical compensation plate is small in the applicable azimuth. Inaddition, the contrast ratio is improved irrespective of the alignmentazimuth of the liquid crystal layer in the present invention, while thecontrast ratio is not improved if the slow axis of the λ/4 plate isgreatly deviated from the alignment azimuth of the liquid crystal layerin the prior art.

It is preferable to make the applicable wavelengths of the λ/4 plate 36and the λ/2 plate 37 different by a value of not less than 20 nm norgreater than 200 nm. The reason why the lower limit is set to 20 nm isthat a difference of less than 20 nm is not very effective in improvingthe contrast ratio and is difficult to control the in-plane retardation.The reason why the upper limit is set to 200 nm is that a difference of200 nm or greater significantly decreases the contrast ratio in theazimuth in which the reflection intensity is minimum, so that leakage oflight cannot be prevented any longer even by application of thereflecting projections and depressions having azimuthal anisotropies onthe reflection intensity.

Further, it is preferable to make the applicable wavelength of the λ/4plate 36 smaller than the applicable wavelength of the λ/2 plate 37. Theλ/4 plate 36 and the λ/2 plate 37 have negative retardations in thethickness direction respectively, but practical negative retardationsdecrease depending on the azimuth in which linearly polarized light isincident, and as a result, most of the retardation of the liquid crystallayer 33 remains. Accordingly, the applicable wavelength of the λ/4plate 36 is made small and the applicable wavelength of the λ/2 plate 37is made large so that the negative retardation occurring in thebroadband λ/4 plate due to an oblique incidence or oblique emissionincreases in the azimuth in which the reflection intensity is maximum.

[Principle Configuration 2]

This liquid crystal display device is configured having, as shown inFIG. 5, a negative retardation plate 39 between the upper glasssubstrate 32 and the λ/4 plate 36 of the principle configuration 1, inwhich the applicable wavelength of the λ/4 plate 36 is made larger thanthe applicable wavelength of the λ/2 plate 37.

When the negative retardation plate 39 having a negative retardation inthe thickness direction, that is, an optical compensation plate exists,the retardation of the negative retardation plate 39 or the retardationof the liquid crystal layer 33 is set so that almost all the retardationof the liquid crystal layer 33 is canceled, and therefore the applicablewavelength of the λ/4 plate 36 is made large and the applicablewavelength of the λ/2 plate 37 is made small so that the retardationsoccurring in these retardation plates due to an oblique incidence oroblique emission decrease in an azimuth in which the reflectionintensity is maximum.

[Principle Configuration 3]

This liquid crystal display device is configured having, as shown inFIG. 6, another λ/2 plate 40 between the λ/2 plate 37 and the polarizingplate 38 of the principle configuration 1, in which slow axes of the λ/4plate 36 and the λ/2 plate 37 are substantially orthogonal to each otherand the applicable wavelength of the λ/2 plate 37 is made larger thanthe applicable wavelength of the other λ/2 plate 40.

In this case, as in the principle configuration 2, it is only requiredthat the applicable wavelength of the λ/4 plate 36 is made large and theapplicable wavelength of the λ/2 plate 37 is made small so that theretardations occurring in these retardation plates due to an obliqueincidence or oblique emission decrease in an azimuth in which thereflection intensity is maximum. However, this applies only to the caseof the λ/4 plate and the λ/2 plate which constitute the broadband λ/4plate, and therefore, in the principle configuration 3, the applicablewavelength of a portion forming the broadband λ/4 plate, that is, theλ/2 plate 37 is made large and the applicable wavelength of the λ/2plate 40 is made small.

SPECIFIC EMBODIMENTS

Based on the above-described main points of the present invention,specific embodiments to which the present invention is applied will bedescribed.

First Embodiment

FIG. 7 and FIG. 8A are cross-sectional views showing a schematicconfiguration of a reflection-type liquid crystal display device of thisembodiment. For convenience here, a λ/4 plate+a λ/2 plate+a polarizingplate are integrally shown in FIG. 7, and a reflecting electrode issimplified and the illustrations of a resin layer and so on are omittedin FIG. 8A.

This liquid crystal display device is constituted such that a lowerglass substrate 21 and an upper glass substrate 22 hold a liquid crystallayer 23, which is composed of liquid crystal molecules having negativedielectric constant anisotropies, sandwiched therebetween, and anoptical compensation plate having a layer structure of a λ/4 plate 1being a first retardation plate, a λ/2 plate 2 being a secondretardation plate, and a polarizing plate 3 (similar to that in FIG. 1)is provided on (a front surface of) the upper glass substrate 22. Notethat the λ/4 plate is a film having a retardation corresponding to aquarter of the wavelength of assumed light (visible light), and the λ/2plate is a film having a retardation corresponding to a half of thewavelength of assumed light (visible light). For example, when thewavelength of the assumed light is 550 nm, the retardation by the λ/4plate is 550/4=137.5 nm, and when the wavelength of the assumed light is600 nm, the retardation by the λ/2 plate is 600/2=300 nm.

The lower glass substrate 21 comprises a TFT element 24 as a switchingelement for each pixel, and a wrinkled reflecting electrode 26 is formedon the surface of the lower glass substrate 21 by forming a pattern inthe shape of projections and depressions or creases using a resin layer25 made of a ultraviolet curing resin or a resist and then covering thesurface with an aluminum layer, and further an alignment film 27 ahaving a vertical alignment property is formed to cover thereflection-type electrode 26. The resin layer 25 is formed in the shapeto cover the TFT elements 24 and the lower glass substrate 21, andpartially patterned for establishing connection for signals from the TFTelements 24. The average tilt angle of the projections and depressionsof the wrinkled reflecting electrode 26 is appropriately set to not lessthan 5° nor greater than 15°.

On the other hand, on the surface of the upper glass substrate 22, anITO transparent electrode 29 is formed through a color filter (CF) layer28, and an alignment film 27 b having a vertical alignment property isformed to cover this transparent electrode 29. Liquid crystal moleculesof the liquid crystal layer 23 are vertically aligned by the alignmentfilms 27 a and 27 b which are in contact with the liquid crystal layer23 at the top and bottom.

Note that a material commercially available from JSR Corp. or NissanChemical Industries, Ltd. is used as the alignment films 27 a and 27 b.Besides, a material commercially available from Merck KGaA is used asthe liquid crystal layer 23. Further, the liquid crystal layer 23 shouldbe vertically aligned where voltage is off, and tilt-aligned wherevoltage is on. In the configuration of FIG. 7, black display is realizedwhere voltage is off, and white display is realized where voltage is on.

Films made by stretching polycarbonate, polystyrene, norbornene resinsare commercialized by several companies, and these are used as materialsfor the λ/4 plate 1 and the λ/2 plate 2 being the retardation plates.For example, films made by stretching the product named Escena Filmmanufactured by Sumitomo Chemical Co., Ltd. and the product named ARTONFilm manufacture by JSR Corp. are commercially available from SumitomoChemical Co., Ltd. or Nitto Denko Corp.

These films are layered in the axial relation shown in FIG. 1, that is,in such a manner that optical axes of both of them are orthogonal toeach other here. The retardation of the λ/2 plate 2 is set to a valueobtained by adding λ/4 to the retardation of the λ/4 plate 1. The λ/2plate 2 and the polarizing plate are layered such that the optical axisof the λ/2 plate 2 and the absorption axis of the polarizing plate forman angle of 45° therebetween.

(Modification)

A modification of the first embodiment will be described now.

FIG. 8B is a cross-sectional view showing a schematic configuration of areflection-type liquid crystal display device of this modification.

In this modification, an optical compensation plate comprises a λ/4plate 11, a λ/2 plate 12, λ/2 plate 13, and a polarizing plate 14, whichare layered in this order as in FIG. 3. The angle between an absorptionaxis of the polarizing plate 14 and an optical axis of the λ/2 plate 13can be changed as a design element, and where this angle is defined asθ, the angle formed between the optical axis of the λ/2 plate 13 and anoptical axis of the λ/2 plate 12 is set to θ±45. In FIG. 3, θ is10°(=25°−15°), so that the angle formed between the optical axis of theλ/2 plate 13 and the optical axis of the λ/2 plate 12 is set to55°=10°+45°. Here, the optical axis of the λ/2 plate 12 is set to80°(=25°+55°).

Further, the optical axis of the λ/2 plate 12 and the optical axis ofthe λ/4 plate 11 are made orthogonal to each other. Here, the opticalaxis of the λ/4 plate 11 is set to 170°(=80°+90°). Combination of theλ/2 plate 13 and the λ/2 plate 12 realizes a λ/4 plate with reversewavelength dispersion. Here, the λ/4 plate and the λ/2 plate are in massproduction to realize the λ/4 with reverse wavelength dispersion and isthus low in cost.

The description until now is made focusing attention only to thein-plane retardation of each retardation plate, while the retardation ina direction of the film thickness is important to realize a wide viewingangle.

The retardation in the thickness direction is expressed by((n_(x)+n_(y))/2−n_(z))·dwhere the refractive indexes within a plane are n_(x), n_(y)(n_(x)≧n_(y)), the refractive index in the thickness direction is n_(z),and the thickness of the film is d.

For a completely uniaxial film (n_(y)=n_(z)), the negative retardationis a half of the in-plane retardation. In the configuration of FIG. 3,the λ/4 plate 11 and the λ/4 plate 12 a realize the negative retardationas a principle configuration, but the absolute value of the negativeretardation is expressed by the sum of negative retardations ofindividual λ/4 plates 11 and 12 a. For this reason, the negativeretardation when using uniaxial films is limited to, for example,λ/4(=λ/4−2×2). We positively employed a biaxial film to optimize thenegative retardation. It was set that 0 nm<A−B<300 nm where Δnd of theliquid crystal layer is A, and the sum of the negative retardations ofthe λ/2 plate 12 and the λ/4 plate 11 is B. Specifically, the design ismade such that A is 300 nm and B is 220 nm±50 nm, whereby excellentcharacteristics can be realized. This excellent range can also beestablished by introducing other indexes.

Excellent characteristics can be obtained when the difference betweenthe retardation of the λ/4 plate 1 in a direction vertical to its planeand the retardation of the liquid crystal molecule is not less than 0 nmnor greater than 200 nm. Similarly, excellent characteristics can beobtained when the difference between the retardations of the λ/2 plate12 and the λ/4 plate 11 in a direction vertical to their planes and theretardation of the liquid crystal molecule is not less than 0 nm norgreater than 200 nm.

The retardations of the λ/4 plate and the λ/2 plate affect the contrastof the liquid crystal display device. Generally, human eyes react togreen light, especially light around 550 nm. For this reason, it isdesirable that the retardation of the λ/2 plate is 550 nm/2=275 nm, andthe retardation of the λ/4 plate is 550 nm/4=137.5 nm. However, theplates, if out of these conditions, seldom cause a problem of decreasein contrast.

FIG. 9 is a characteristic diagram showing front contrast dependencewhen the in-plane retardation of the λ/4 plate deviates from this 137.5nm.

A front contrast of about 5 or greater is realized within a range of notless than 100 nm nor greater than 180 nm. It can be said that, for thereflection-type liquid crystal display device, a contrast of 5 orgreater causes no problem in practical use. From this fact, the range ofthe in-plane retardation was set to a range of not less than 100 nm norgreater than 180 nm. In this embodiment, that principle is common to therange of the value of λ/4, and therefore when the λ/4 plate wasemployed, substantially excellent characteristics could be obtained inthis range in common.

Similarly, the result of verification of the λ/2 plate is shown in FIG.10.

Although an ideal retardation of the λ/2 plate is 275 nm, the contrastwhen out of this value is shown. A front contrast of about 5 or greateris realized where the retardation is within a range of not less than 200nm nor greater than 360 nm. It can be said that, for the reflection-typeliquid crystal display device, a contrast of not less than 5 causes noproblem in practical use. From this fact, the range of the in-planeretardation is set to a range of not less than 200 nm nor greater than360 nm. In this embodiment, that principle is common to the range of thevalue of λ/2, and therefore when the λ/2 plate is employed,substantially excellent characteristics can be obtained in this range incommon.

This value as the retardation is also in common to the value of each ofλ/4 and λ/2 as a difference between the retardations of films. Forexample, it is described in this description that the difference inretardation between the λ/4 plate and the λ/2 plate is λ/4, and the samediscussion as above also applies to this value.

The relation between the absorption axis of the polarizing plate and thealignment direction of the liquid crystal layer affects the viewingangle characteristics of the liquid crystal display. The viewing anglecharacteristics depend on the Δnd of the liquid crystal layer, thein-plane retardations of films, especially, the retardations of the λ/4plate 1 and the λ/4 plate 11 as negative retardation plates. The optimalangle of the polarizing plate to allow the viewing angle characteristicsvertically and laterally symmetrical where the alignment direction ofthe liquid crystal layer is the lateral direction is shown in FIG. 11.The Δnd of the liquid crystal layer is X, the negative retardation ofthe film taken as the prior art example is Y, and the difference betweenX and Y is set as the horizontal axis. Here, as for the negativeretardation, the negative retardation composed from the λ/4 plate 1 andthe λ/4 plate 2 a, or that from the λ/4 plate 11 and the λ/4 12 a platealso functions as Y which is a base of this index.

The relation between this difference in retardation and the optimalangle of the polarizing plate is shown in FIG. 11. It is shown that theoptimal angle is almost on a line expressed by Optimal angle(°)=(retardation of liquid crystal layer (nm)−negative retardation offilm (nm))·22.5/300−7.5. Here, to perform white display, the retardationof the liquid crystal layer needs to have about λ/4=137.5 nm or greater.In this case, the calculation in consideration of no negativeretardation given by a film results in about 2°. This shows that the setangle of the polarizing plate is desirably 0 degrees or greater.Further, it is advantageous that the retardation of the liquid crystallayer is large in order to perform white display. Where the retardationis 500 nm, the device can be driven at a low voltage of about 3V. Here,suppose that the negative retardation of the film is 0, the angle of thepolarizing plate is 30°. From these verification results, the angle ofthe polarizing plate is set to a range of not less than 0° nor greaterthan 30° in this embodiment.

Besides, when the difference between the values of the retardation (nm)of the liquid crystal layer and the negative retardation (nm) of thefilm is too large, the contrast at an oblique viewing angle decreases,leading to poor viewing angle characteristics. This difference is set to200 nm or less, whereby the range of a tilt angle where the contrast is3 or greater in all azimuths can be set to ±40°.

As has been described, according to this embodiment, it becomes possibleto realize bright display and a liquid crystal display device with awide viewing angle.

Second Embodiment

Projections and depressions having reflecting ability on the surface areformed on a substrate surface as described below. First, aphotosensitive resin (manufactured by Shipley Far East Ltd.) is appliedby spin coating in a thickness of about 1 μm onto a TFT substrate (lowerglass substrate). After prebake, ultraviolet irradiation, first bake,and second bake are sequentially performed to form projections anddepressions with average tilt angles of 4.5° (Sample 1, ComparativeExample 1), 7.5° (Sample 2, Comparative Example 2), 11.5° (Sample 3,Comparative Example 3), and 14.5° (Sample 4, Comparative Example 4). Itshould be noted that the control of the tilt angle of the projectionsand depressions is conducted by changing the period of the first bake,and the average tilt angle is measured through use of an atom forcemicroscope (AFM). Thereafter, Al is deposited onto the projections anddepressions to form reflecting projections and depressions.

Next, a vertical alignment film (manufactured by JSR Corp.) is appliedto the surface of the TFT substrate and a CF substrate (upper glasssubstrate), spacers with a diameter of 3 μm (Manufactured by SekisuiFine Chemical Co., Ltd.) are scattered, and bonding is performed. Intothis vacant panel, liquid crystal (manufactured by Merck Japan Ltd.),which has a negative dielectric constant anisotropy and a refractiveindex difference Δn between abnormal light and normal light of 0.0995,is injected to obtain a reflection-type liquid crystal display device inthe VA mode.

FIG. 12 and FIG. 13 show a method for estimating the retardation of theliquid crystal layer where no voltage is applied and the retardation ofthe retardation plate, shown from an observation angle of 0° in FIG. 12,and an observation angle of 45° in FIG. 13. In FIGS. 12 and 13, anincident angle θ on the liquid crystal decreases by 0→ξ as the enteringlight approaches from the upper substrate toward the lower substrate(see the arrow to the left of the optical path), and the incident angleθ on the liquid crystal decreases by 0→ξ as the reflected light travelsfrom the lower substrate toward the upper substrate to the right of theoptical path (see the arrow to the right of the optical path). In FIG.12, the optical path length of the entering light along oath VAC (vacuumair compensation layer) is dv/cos θ2=dv/cos2ξ, and the optical oathlength in the liquid crystal is dlc/cos2ξ. The reflected light passesthrough a return route in which the optical path length through thecompensation layer, air and vacuum is dv, and the optical path lengththrough the liquid crystal is dlc. In FIG. 13, the optical path lengthof the entering light along path VAC is dv/cos θ2, and the optical pathlength in the liquid crystal is =dlc/cos θ2. The reflected light passesthrough a return route in which the optical path length through thecompensation layer air and vacuum is dv/cos(θ2−2ξ), and the optical pathlength through the liquid crystal is dlc/cos(θ2−2ξ). FIGS. 14A-14D showa method for finding a refractive index anisotropy when light isincident, tilting θ from a Z axis, on the liquid crystal and retardationplate.

The incident angles of light emitted at observation angles of 0° and 45°are defined by the average tilt angle, and liquid crystal molecules aretilt-aligned at the average tilt angle as approaching from the uppersubstrate toward the lower substrate (reflector side), so that theincident angle of light on the liquid crystal decreases by the averagetilt angle as approaching from the upper glass substrate toward thelower glass substrate in an approach route, and decreases by the averagetilt angle as approaching from the lower glass substrate toward theupper glass substrate in a return route. Further, assuming that theliquid crystal is an index ellipsoid having a positive refractive indexanisotropy in the substrate vertical direction, the retardation of theliquid crystal layer where no voltage was applied was obtained from therefractive index anisotropy when light was incident tilting by theincident angle from the Z-axis direction.

FIGS. 14A and 14B assume that the retardation plate has characteristicsof an index ellipsoid having negative refractive index anisotropy in thesubstrate vertical direction, FIG. 14A showing the incident light in athree-dimensional configuration, and FIG. 14B showing the incident lightin two-dimensions. FIGS. 14C and 14D assume that the liquid crystal hascharacteristics of an index ellipsoid having positive refractive indexanisotropy in the substrate vertical direction, FIG. 14C showing theincident light in a three-dimensional space, and FIG. 14D showing theincident light in two dimensions.

The apparent refractive indices nx′, nxy, nz′ when light is incident, atin incident angle of θ on the xy plane, correspond to the cut surface ofan ellipsoid rotated minus θ from the axis. Accordingly, nx=nx, ny′, nz′can be found by the following equations:

${\frac{Y^{2}}{{Ny}^{2}} + \frac{Z^{2}}{{Nz}^{2}}} = 1$${\frac{{Ny}^{\prime 2}\cos^{2}\theta}{{Ny}^{2}} + \frac{{Ny}^{\prime 2}\sin^{2}\theta}{{Nz}^{2}}} = 1$${Ny}^{2\prime} = \frac{1}{\frac{\cos^{2}\theta}{{Ny}^{2}} + \frac{\sin^{2}\theta}{{Nz}^{2}}}$${Ny}^{\prime} = {\frac{NyNz}{\sqrt{{{Nz}^{2}\cos^{2}\theta} + {{Ny}^{2}\sin^{2}\theta}}} = {\frac{Nz}{\sqrt{{\frac{{Nz}^{2}}{{Ny}^{2}}\cos^{2}\theta} + \left( {1 - {\cos^{2}\theta}} \right.}} = \frac{Nz}{\sqrt{1 - {v\;\cos^{2}\theta}}}}}$${\text{However,}\mspace{11mu} v} = \frac{{Ny}^{2} - {Nz}^{2}}{{Ny}^{2}}$  When  Nz^(′)  is  similarly  found                                                  ${\frac{Y^{2}}{{Ny}^{2}} + \frac{Z^{2}}{{Nz}^{2}}} = 1$${\frac{{Ny}^{\prime 2}\sin^{2}\theta}{{Ny}^{2}} + \frac{{Ny}^{\prime 2}\cos^{2}\theta}{{Nz}^{2}}} = 1$${Ny}^{\prime} = {\frac{NyNz}{\sqrt{{{Nz}^{2}\sin^{2}\theta} + {{Ny}^{2}\cos^{2}\theta}}} = {\frac{Nz}{\sqrt{{\frac{{Nz}^{2}}{{Ny}^{2}}\left( {1 - {\cos^{2}\theta}} \right)} + {\cos^{2}\theta}}} = \frac{Nz}{\sqrt{\frac{{Nz}^{2}}{{Ny}^{2}} + {v\;\cos^{2}\theta}}}}}$

Table 1 shows the retardations in the substrate vertical direction ofthe retardation plates used in this embodiment, and Table 2 and Table 3show results of calculation for every observation angle of theretardations of the liquid crystal layers where no voltage is appliedwhen the reflecting projections and depressions with the average tiltangles of not less than 3.5° nor greater than 15.5° are applied, and theretardations of the retardation plates. The retardations of the liquidcrystal layers where no voltage is applied are 4.5 nm at the averagetilt angle of 4.5°, 12.6 nm at 7.5°, 30.5 nm at 11.5°, and 50.1 nm at14.5° for the observation angle of 0°, and are 98.3 nm at the averagetilt angle of 4.5°, 77.4 nm at 7.5°, 56.5 nm at 11.5°, and 45.5 nm at14.5° for the observation angle of 45°.

TABLE 1 Retardations in substrate vertical direction of retardationplates {circle around (1)} to {circle around (8)} (nm) Retar- Retar-Retar- Retar- Retar- Retar- Retar- Retar- dation dation dation dationdation dation dation dation {circle around (1)} {circle around (2)}{circle around (3)} {circle around (4)} {circle around (5)} {circlearound (6)} {circle around (7)} {circle around (8)} Rf 47.5 103.6 132.8154.3 175.1 195.1 248.1 288.4 Rf/Rlc 0.16 0.35 0.44 0.52 0.59 0.65 0.830.97

TABLE 2 Estimation results of retardations of liquid crystal layerswhere no voltage is applied and retardations of retardation plates (atobservation angle of 0°) Liquid Retar- Retar- Retar- Retar- Retar-Retar- Retar- Retar- Average crystal dation dation dation dation dationdation dation dation tilt layer {circle around (1)} {circle around (2)}{circle around (3)} {circle around (4)} {circle around (5)} {circlearound (6)} {circle around (7)} {circle around (8)} Sample 1 3.5 2.7 3.94.9 4.6 4.9 5.3 4.7 6.5 7.2 4.5 4.5 4.4 5.9 5.9 6.5 7.0 6.6 8.9 10.0 5.56.7 4.9 7.2 7.5 8.4 9.2 9.0 12.0 13.6 6.5 9.4 5.6 8.7 9.5 10.7 11.8 11.915.7 17.9 Sample 2 7.5 12.6 6.5 10.5 11.8 13.3 14.8 15.3 20.0 22.9 8.516.3 7.4 12.6 14.5 16.4 18.3 19.3 25.0 28.7 9.5 20.5 8.5 15.0 17.5 20.022.3 23.7 30.7 35.3 Sample 3 10.5 25.2 9.7 17.6 20.9 23.9 26.8 28.7 37.042.6 11.5 30.5 11.1 20.5 24.7 28.3 31.7 34.2 44.0 50.8 12.5 36.4 12.623.8 28.8 33.1 37.2 40.3 51.8 59.8 Sample 4 13.5 42.9 14.2 27.3 33.438.4 43.2 47.0 60.3 69.7 14.5 50.1 16.0 31.2 38.3 44.2 49.8 54.3 69.680.5 15.5 57.9 17.9 35.5 43.8 50.5 56.9 62.3 79.7 92.3

TABLE 3 Estimation results of retardations of liquid crystal layerswhere no voltage is applied and retardations of retardation plates (atobservation angle of 45°) Liquid Retar- Retar- Retar- Retar- Retar-Retar- Retar- Retar- Average crystal dation dation dation dation dationdation dation dation tilt layer {circle around (1)} {circle around (2)}{circle around (3)} {circle around (4)} {circle around (5)} {circlearound (6)} {circle around (7)} {circle around (8)} Sample 1 3.5 106.425.0 47.3 64.1 73.7 83.0 90.2 104.6 123.6 4.5 98.3 23.8 44.6 62.0 71.380.3 87.1 101.8 119.0 5.5 90.8 22.7 42.2 60.1 69.0 77.6 84.2 98.6 114.76.5 83.9 21.7 40.1 58.2 66.8 75.2 81.4 95.8 110.6 Sample 2 7.5 77.4 20.938.3 56.4 64.7 72.8 78.8 93.2 106.7 8.5 71.5 20.2 36.8 54.7 62.7 70.576.3 90.7 103.0 9.5 66.0 19.6 35.5 53.0 60.8 68.4 73.9 88.3 99.4 Sample3 10.5 61.0 19.1 34.4 51.5 59.1 66.4 71.7 86.1 96.1 11.5 56.5 18.7 33.650.1 57.4 64.5 69.6 84.0 93.0 12.5 52.4 18.5 33.1 48.7 55.9 62.7 67.682.0 90.1 Sample 4 13.5 48.7 18.4 32.9 47.5 54.4 61.1 65.7 84.6 87.414.5 45.5 18.4 32.8 46.3 53.0 59.5 64.0 82.4 84.8 15.5 42.8 18.5 33.145.2 51.8 58.1 62.4 80.4 82.5

Further, assuming that the retardation plate is an index ellipsoidhaving a negative refractive index anisotropy in the substrate verticaldirection, the retardation was obtained, in a similar manner to that ofthe liquid crystal, from the refractive index anisotropy when light wasincident tilting by the incident angle from the Z-axis direction. Theincident angles of light emitted at observation angles of 0° and 45° aredefined by the average tilt angle, but since the retardation plate isnot tilt-aligned unlike the liquid crystal, the values of the incidentangles can be used as they are.

It should be noted that the retardation plates have retardations in thesubstrate vertical direction of {circle around (1)} 47 nm, {circlearound (2)} 104 nm, {circle around (3)} 133 nm, {circle around (4)} 154nm, {circle around (5)} 175 nm, {circle around (6)} 195 nm, {circlearound (7)} 248 nm, and {circle around (8)} 288 nm respectively. Theretardation plates {circle around (1)} to {circle around (8)} haveretardations as shown in Table 1, and, for the observation angle of 0°,the optimal retardation plate is {circle around (1)} at the average tiltangle of 4.5°, {circle around (4)} at 7.5°, {circle around (5)} at11.5°, and {circle around (5)} at 14.5°. On the other hand, for theobservation angle of 45°, the optimal retardation plate is {circlearound (7)} at the average tilt angle of 4.5°, {circle around (6)} at7.5°, {circle around (4)} at 11.5°, and {circle around (3)} at 14.5°.The application of optimal retardation plates at the respective averagetilt angles for the observation angle of 0° leads to deviation incompensation conditions at the observation angle of 45°, and theretardation is 74.5 nm at the average tilt angle of 4.5°, 12.7 nm at7.5°, 8.0 nm at 11.5°, and 14.0 nm at 14.5°. On the other hand, theapplication of optimal retardation plates at the respective average tiltangles for the observation angle of 45° leads to deviation incompensation conditions at the observation angle of 0°, and theretardation is 4.4 nm at the average tilt angle of 4.5°, 2.7 nm at 7.5°,2.2 nm at 11.5°, and 11.8 nm at 14.5°.

In the case in which the optimal retardation greatly differs dependingon the observation angle, light greatly leaks at a specific angle unlessa retardation plate is selected with priority given to a largerretardation of the liquid crystal layer where no voltage is applied,resulting in a great loss of contrast characteristics. Accordingly, itis preferable to determine that the optimal retardation plate is {circlearound (7)} at the average tilt angle of 4.5°, {circle around (6)} at7.5°, {circle around (4)} at 11.5°, {circle around (3)} or {circlearound (5)} at 14.5°.

Accordingly, the optimal retardation necessary for compensation shown bythe ratio between the cell thickness of the liquid crystal layer and theretardation Rlc obtained from birefringence difference is 0.83 at theaverage tilt angle of 4.5°, 0.65 at 7.5°, 0.52 at 11.5°, and 0.44 or0.59 at 14.5°. The value of Rf/Rlc varies with the average tilt angle ofthe reflecting projections and depressions, and sufficient compensationeffect can be expected even with deviation of about 10% from the optimalretardation, resulting in 0.6≦Rf/Rlc≦0.9 for the average tilt angle ofnot less than about 4° nor greater than about 6°, 0.5≦Rf/Rlc≦0.8 for notless than about 7° nor greater than about 9°, and 0.4≦Rf/Rlc≦0.7 for notless than about 10° nor greater than about 15°.

Here, the average tilt angle is expressed by integral numbers, but whenthere is a decimal fraction, it only needs to be rounded off so that thedescription of the average tilt angle of not less than 4° nor greaterthan 6° equals the average tilt angle of not less than 3.5° nor greaterthan 6.5°. Suppose that the deviation up to ±10% from the optimalretardation is within the optimal retardation range, the retardation isnot less than about 225 nm nor greater than about 275 nm (not less than0.75 nor greater than 0.92) at the average tilt angle of 3.5° and is notless than about 180 nm nor greater than about 220 nm (not less than 0.60nor greater than 0.74) at 6.5°, and as a result, the optimal retardationrange is 0.6≦Rf/Rlc≦0.9 for the average tilt angle of not less thanabout 4° nor greater than about 6°.

Here, the Rf/Rlc is expressed by values at a first decimal place, but avalue at a second decimal place or lower only needs to be rounded off sothat the range of 0.6≦Rf/Rlc≦0. 9 is equal to the range of0.55≦Rf/Rlc≦0.94.

Similarly, the optimal retardation range is not less than about 140 nmnor greater than about 195 nm (not less than 0.47 nor greater than 0.65)at the average tilt angle of 9.5°, and the optimal retardation range is0.5≦Rf/Rlc≦0.8 at the average tilt angle of not less than about 7° norgreater than about 9°. Similarly the optimal retardation range is notless than about 120 nm nor greater than about 195 nm (not less than 0.40nor greater than 0.65) at the average tilt angle of 15.5°, and theoptimal retardation range is 0.4≦Rf/Rlc≦0.7 for the average tilt angleof about 10° to about 15°.

Configuration is made such that the retardation plate uniaxiallystretched to have thus obtained retardation is layered, in an orthogonalplacement, between a polarizing plate and a liquid crystal displayelement. More specifically, it is only required to layer, in anorthogonal placement, between the polarizing plate and the liquidcrystal display element, a retardation plate having a retardation of 260nm in the substrate in-plane direction and a retardation of 125 nm inthe substrate vertical direction (manufactured by Sumitomo Chemical Co.,Ltd., n_(z) coefficient=0.94) in Sample 1 since the optimal retardationis about 248 nm at the average tilt angle of 4.5°, a retardation platehaving a retardation of 220 nm in the substrate in-plane direction and aretardation of 97.9 nm in the substrate vertical direction (manufacturedby Sumitomo Chemical Co., Ltd., n_(z) coefficient=0.94) in Sample 2since the optimal retardation is about 195 nm at the average tilt angleof 7.5°, a retardation plate having a retardation of 165 nm in thesubstrate in-plane direction and a retardation of 75.1 nm in thesubstrate vertical direction (manufactured by Sumitomo Chemical Co.,Ltd., n_(z) coefficient=0.96) in Sample 3 since the optimal retardationis about 154 nm at the average tilt angle of 11.5°, and a retardationplate having a retardation of 150 nm in the substrate in-plane directionand a retardation of 66.4 nm in the substrate vertical direction(manufactured by Sumitomo Chemical Co., Ltd., n_(z) coefficient=0.94) inSample 4 since the optimal retardation is about 133 nm at the averagetilt angle of 14.5°, respectively.

However, as shown in FIG. 15, necessary retardation plates, in additionto this retardation plate, for use in the reflection-type liquid crystaldisplay device are a retardation plate (λ/2 plate) having a retardationof about a half of the visible light wavelength in the substratein-plane direction and a retardation plate (λ/4 plate) having aretardation of about a quarter of the same which are as a broadband λ/4plate, and consequently four retardation plates altogether includingcompensation plates (1) and (2) which are layered in an orthogonalplacement are required. A larger number of layered retardation platesreduces the advantage of use of inexpensive ones, and thus the λ/4 plateand the compensation plate (1) are integrated to form a configurationwith three retardation plates in the embodiment. Here, the liquidcrystal layer is regarded as existing between the reflector and thecompensation plate (2), and the illustration thereof is omitted in FIG.15 for convenience.

In other words, the retardation in the substrate in-plane direction ofthe λ/4 plate is about 135 nm, to which the retardation of onecompensation plate is added to enable the integration, resulting in 395nm at the average tilt angle of 4.5°, 355 nm at 7.5°, 300 nm at 11.5°,and 285 nm at 14.5°. As the integrated retardation plates, a retardationplate having retardations of 400 nm in the substrate in-plane directionand 178 nm in the substrate vertical direction (Sample 1, manufacturedby Sumitomo Chemical Co., Ltd., n_(z) coefficient=0.94) at the averagetilt angle of 4.5°, a retardation plate having retardations of 350 nm inthe substrate in-plane direction and 155 nm in the substrate verticaldirection (Sample 2, manufactured by Sumitomo Chemical Co., Ltd., n_(z)coefficient=0.94) at 7.5°, a retardation plate having retardations of300 nm in the substrate in-plane direction and 133 nm in the substratevertical direction (Sample 3, manufactured by Sumitomo Chemical Co.,Ltd., n_(z) coefficient=0.94) at 11.5°, and a retardation plate havingretardations of 288 nm in the substrate in-plane direction and 128 nm inthe substrate vertical direction (Sample 4, manufactured by SumitomoChemical Co., Ltd., n_(z) coefficient=0.94) at 14.5°, are usedrespectively.

Here, the integrated retardation plate has a retardation in thesubstrate vertical direction, but the retardation effective incompensating the retardation of the liquid crystal layer where novoltage is applied is the retardation substantially corresponding tothat of the compensation plate. This is because light incident on thebroadband λ/4 plate is incident in linearly polarized light from anazimuth of about 45° with respect to its slow axis, while light incidenton the compensation plate is incident in a circularly polarized lightwith no azimuth dependence on the slow axis. In other words, theretardation in the substrate vertical direction of the uniaxiallystretched retardation plate has azimuth dependence and thus effectivelyacts in the azimuth of the slow axis, but does not act so effectively inan azimuth greatly deviated from that of the slow axis. The films andplates are arranged in layers in order such that the absorption axis ofthe polarizing plate is in an azimuth of 15°, the slow axis of the λ/2plate is in an azimuth of 25°, the slow axis of the integral typeretardation plate (λ/4 plate+compensation plate (1)) is in an azimuth of80°, the compensation plate (2) is in an azimuth of 170°, and therubbing angle of the liquid crystal is in an azimuth of 0°, therebyobtaining a reflection-type liquid crystal display device.

Besides, as a comparative example, a compensation plate is constitutedof a biaxially stretched retardation plate to produce a reflection-typeliquid crystal display device in which the retardation is set so thatobliquely incident light becomes circularly polarized light whenreaching the reflector, that is, retardations occurring in theretardation plate and the liquid crystal layer in an approach route areequal to each other. Table 4 and Table 5 show results of calculation forevery observation angle of the retardations of the liquid crystal layersin the approach route when the reflecting projections and depressionswith the average tilt angles of not less than 3.5° nor greater than15.5° are applied, and the retardations of the retardation plates.

TABLE 4 Estimation results of retardations of liquid crystal layers inapproach route and retardations of retardation plates (at observationangle of 0°) Liquid Retar- Retar- Retar- Retar- Retar- Retar- Retar-Retar- Average crystal dation dation dation dation dation dation dationdation tilt layer {circle around (1)} {circle around (2)} {circle around(3)} {circle around (4)} {circle around (5)} {circle around (6)} {circlearound (7)} {circle around (8)} Comparative 3.5 2.3 3.9 4.9 4.6 4.9 5.34.7 6.5 7.2 Example 1 4.5 3.9 4.4 5.9 5.9 6.5 7.0 6.6 8.9 10.0 5.5 5.84.9 7.2 7.5 8.4 9.2 9.0 12.0 13.6 6.5 8.2 5.6 8.7 9.5 10.7 11.8 11.915.7 17.9 Comparative 7.5 11.0 6.5 10.5 11.8 13.3 14.8 15.3 20.0 22.9Example 2 8.5 14.2 7.4 12.6 14.5 16.4 18.3 19.3 25.0 28.7 9.5 18.0 8.515.0 17.5 20.0 22.3 23.7 30.7 35.3 Comparative 10.5 22.1 9.7 17.6 20.923.9 26.8 28.7 37.0 42.6 Example 3 11.5 26.8 11.1 20.5 24.7 28.3 31.734.2 44.0 50.8 12.5 32.0 12.6 23.8 28.8 33.1 37.2 40.3 51.8 59.8Comparative 13.5 37.8 14.2 27.3 33.4 38.4 43.2 47.0 60.3 69.7 Example 414.5 44.2 16.0 31.2 38.3 44.2 49.8 54.3 69.6 80.5 15.5 51.3 17.9 35.543.8 50.5 56.9 62.3 79.7 92.3

TABLE 5 Estimation results of retardations of liquid crystal layers inapproach route and retardations of retardation plates (at observationangle of 45°) Liquid Retar- Retar- Retar- Retar- Retar- Retar- Retar-Retar- Average crystal dation dation dation dation dation dation dationdation tilt layer {circle around (1)} {circle around (2)} {circle around(3)} {circle around (4)} {circle around (5)} {circle around (6)} {circlearound (7)} {circle around (8)} Comparative 3.5 44.8 9.8 17.8 28.0 32.236.2 39.1 50.3 58.1 Example 1 4.5 38.9 8.6 15.1 25.9 29.7 33.4 36.1 46.453.6 5.5 33.5 7.5 12.7 23.9 27.4 30.8 33.2 42.7 49.2 6.5 28.6 6.5 10.622.0 25.2 28.3 30.4 39.1 45.1 Comparative 7.5 24.1 5.7 8.8 20.2 23.125.9 27.7 35.8 41.2 Example 2 8.5 20.1 5.0 7.3 18.5 21.1 23.7 25.2 32.637.5 9.5 16.6 4.4 6.0 16.9 19.3 21.5 22.8 29.6 34.0 Comparative 10.513.4 3.9 4.9 15.4 17.5 19.5 20.6 26.7 30.7 Example 3 11.5 10.7 3.6 4.214.0 15.8 17.6 18.5 24.0 27.6 12.5 8.4 3.3 3.6 12.6 14.3 15.9 16.5 21.524.6 Comparative 10.5 6.4 3.2 3.3 11.4 12.8 14.2 14.7 19.2 21.9 Example4 11.5 4.9 3.2 3.3 10.2 11.5 12.7 13.0 17.0 19.4 12.5 3.7 3.3 3.6 9.110.2 11.2 11.4 15.0 17.0

The retardations occurring in the liquid crystal layers in the approachroute are 3.9 nm at the average tilt angle of 4.5°, 11.0 nm at 7.5°,26.8 nm at 11.5°, and 44.2 nm at 14.5° for the observation angle of 0°,and 38.9 nm at the average tilt angle of 4.5°, 24.1 nm at 7.5°, 10.7 nmat 11.5°, and 4.9 nm at 14.5° for the observation angle of 45°.Accordingly, for the observation angle of 0°, the optimal retardationplate is {circle around (1)} at the average tilt angle of 4.5°, {circlearound (2)} at 7.5°, {circle around (4)} at 11.5°, and {circle around(4)} at 14.5° . On the other hand, for the observation angle of 45°, theoptimal retardation plate is {circle around (6)} at the average tiltangle of 4.5°, {circle around (4)} at 7.5°, {circle around (3)} at11.5°, and {circle around (2)} at 14.5°.

In the case in which the optimal retardation greatly differs dependingon the observation angle, light greatly leaks at a specific angle unlessa retardation plate is selected with priority given to a largerretardation of the liquid crystal layer where no voltage is applied,resulting in a great loss of contrast characteristics. Accordingly, itis preferable to determine that the optimal retardation plate is {circlearound (6)} at the average tilt angle of 4.5°, {circle around (4)} at7.5°, {circle around (3)} at 11.5°, and {circle around (4)} at 14.5°.The optimal retardation plate is {circle around (7)} at the average tiltangle of 4.5°, {circle around (6)} at 7.5°, {circle around (4)} at11.5°, and {circle around (3)} or {circle around (5)} at 14.5° in theembodiment, which shows that the optimal retardation plates aredifferent from the above respectively.

Accordingly, a retardation plate having retardations of 3 nm in thesubstrate in-plane direction and 195 nm in the substrate verticaldirection (Comparative Example 1, manufactured by Sumitomo Chemical Co.,Ltd., n_(z) coefficient=102) at the average tilt angle of 4.5°, aretardation plate having retardations of 3 nm in the substrate in-planedirection and 155 nm in the substrate vertical direction (ComparativeExamples 2 and 4, manufactured by Sumitomo Chemical Co., Ltd., n_(z)coefficient=102) at 7.5° and 14.5°, and a retardation plate havingretardations of 3 nm in the substrate in-plane direction and 133 nm inthe substrate vertical direction (Comparative Example 3, manufactured bySumitomo Chemical Co., Ltd., n_(z) coefficient=102) at 11.5°, are usedas compensation plates respectively.

The contrast ratio in all white/all black display of the reflection-typeliquid crystal display device produced in each of Samples andComparative Examples was measured at an observation azimuth of 90° andobservation angles of 0° and 45° using a diffused light source. Theirresults are shown in Table 6 and Table 7. The contrast ratios of Samples1 to 4 are about 25 or greater at both observation angles (however, thecontrast ratio at the observation angle of 0° is 20 at the average tiltangle of 14.5° because priority is given to the observation angle of45°), exhibiting excellent contrast characteristics at almost allangles. On the other hand, the contrast ratios of Comparative Examples 1to 4 are about 22 or less at the observation angle of 45°, so that thecontrast ratio is decreased by about 15% as compared to the examples.This is because the estimation of the optimal retardation deviates byabout 15% in Comparative Examples.

TABLE 6 Contrast ratios of Samples 1 to 4 Observation Example 1 Example2 Example 3 Example 4 Angle 4.5° 7.5° 11.5° 14.5°  0° 27 25 25 20 45° 2625 25 26

TABLE 7 Contrast ratios of Comparative Examples 1 to 4 ConventionalConventional Conventional Conventional Observation Example 1 Example 2Example 3 Example 4 Angle 4.5° 7.5° 11.5° 14.5°  0° 27 25 25 22 45° 2221 21 22

As has been described, according to this embodiment, display with lessviewing angle dependence and a high contrast ratio can be obtained, sothat display becomes easy to view even in a relatively dim place such asan indoor environment. This leads to wider application of thereflection-type liquid crystal display device and greatly contributes tomarket expansion.

Third Embodiment

FIG. 16 is a perspective view showing a configuration of a singlepolarizing plate and a measurement method. Here, only a reflector and apolarizing plate are shown in FIG. 16 for convenience.

The polarizing plate (manufactured by Sumitomo Chemical Co., Ltd.) wasarranged above the reflector such that its absorption axis was in a 0°azimuth (its transmission axis in a 90° azimuth), and the reflectionintensity was measured with the azimuth angle of a 30° incidence varied.Here, the reflector is made by forming projections and depressions usinga resist (manufactured by Shipley Ltd.) on a glass substrate, anddepositing an aluminum film on their surfaces. Note that the reflectorin use was a non-directional reflector in which tilt surfaces of thereflecting projections and depressions are oriented toward randomazimuths to check the azimuth characteristics due to the polarizingplate.

FIG. 17 is a characteristic diagram showing azimuth anglecharacteristics of the single polarizing plate.

The reflection intensity is minimum in the azimuth of the absorptionaxis and the reflection intensity is maximum in the azimuth of thetransmission axis due to the absorption characteristics of thepolarizing plate.

On the other hand, FIG. 18 is a perspective view showing a configurationof a polarizing plate+λ/4 and a measurement method. Here, only thereflector, λ/4 plate, and polarizing plate are shown in FIG. 18 forconvenience.

A retardation plate having a wavelength of a quarter of the visiblelight wavelength (manufactured by Sumitomo Chemical Co., Ltd., lowwavelength dispersion film, in-plane retardation of 138 nm) was arrangedbetween the polarizing plate and the reflector such that the angleformed between its slow axis and absorption axis was 45°, and thereflection intensity was measured with the azimuth angle of a 30°incidence and a 0° light-reception varied.

FIG. 19 is a characteristic diagram showing azimuth anglecharacteristics of the polarizing plate+λ/4.

Originally, when arrangement is made such that the angle formed betweenthe slow axis of the retardation plate and the absorption axis of thepolarizing plate is 45°, the reflection intensity should be minimum inthe azimuth of the transmission axis and the azimuth of the absorptionaxis since linearly polarized light incident from the azimuth of thetransmission axis is rotated 90° to be parallel to the absorption axisof the polarizing plate. However, the reflection intensity is actuallyminimum in the azimuths deviated by about −15° from the respectiveazimuths.

FIG. 20 is a characteristic diagram showing azimuth anglecharacteristics of a λ/4 polarizing plate, for every incident angle(0-30° incidence), of the reflection intensity measured with theincident angle and the azimuth angle varied in the same configuration asin FIG. 18. With an increase in incident angle, the azimuth in which thereflection intensity is minimal increasingly deviates to a minusazimuth.

The increase in the reflection intensity due to azimuth deviation up toθ1=10° is small, but when θ1 is greater than that, the increase in thereflection intensity due to azimuth deviation becomes large, leading toa decrease in CR. This is because the deviation of retardation increaseswith an increase in incident angle so that the polarization azimuthincreasingly deviates from 90° rotation.

FIG. 21 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 270°, and the incident angle and therotation angle of the axis placement were varied in the sameconfiguration as in FIG. 18.

The reason why the observation azimuth is fixed to 270° here is that theobservation azimuth, that is, the azimuth in which the reflectionintensity due to the reflecting projections and depressions is high(directional azimuth) is set to 90° and 270°, and the rotation angle ofthe axis placement by which the reflection intensity becomes minimum inthe azimuths is found. On the other hand, when the axis placement isrotated +15° in an azimuth opposite to the deviation of the polarizationazimuth, the polarization azimuth becomes substantially parallel to theabsorption axis of the polarizing plate because of offset by the amountof deviation of the polarization azimuth, so that the reflectionintensity becomes minimum within the whole incident angle range.However, the reflection intensity is low as compared with that beforerotation within the range of not less than 0° nor greater than 25°, andtherefore improvement effects can be expected.

FIG. 22 is a characteristic diagram showing λ/4 polarizing plate azimuthangle characteristics (30° incidence) of the reflection intensitymeasured when the axis placement was rotated +15° from the configurationin FIG. 18, and the azimuth angle of a 30° incidence was varied.

Here, when the axis placement is rotated +15° in an azimuth opposite tothe Deviation, the reflection intensity becomes minimum in thedirectional azimuth (90°, 270°) by rotating the axis placement +15°.

FIG. 23 is a characteristic diagram showing λ/4 polarizing plate azimuthangle characteristics (30° incidence) of measured contrast ratio (CR) asin FIG. 22.

When the axis placement is rotated +15° in an azimuth opposite to thedeviation, the azimuth of the transmission axis deviates by +15° fromthe directional azimuth to slightly decrease the reflection intensity ofwhite display, but the decreased rate is very small, and as a result,the contrast ratio is maximum in the directional azimuth (90°, 270°).Accordingly, a polarizing plate and a retardation plate having aretardation of about a quarter of the visible light wavelength in thesubstrate in-plane direction are arranged such that the angle formedbetween an azimuth φ in which the reflection intensity is maximum and anabsorption axis P of the polarizing plate is not less than about 65° norgreater than about 90°, and the angle formed between a slow axis F1 ofthe retardation plate and P is about 45°, whereby the contrast ratio canbe improved in the directional azimuth to realize display that is easyto view. The reason why the angle formed between φ and P is set here tonot less than 65° nor greater than 90° is that although an angle of 75°is optimal as the embodiment, an angle within this range allows thereflection intensity to be low as compared to that before the rotation,so that improvement effects can be expected.

FIG. 24 is a characteristic diagram showing azimuth anglecharacteristics of the reflection intensity measured when a retardationplate having λ/4 of the visible light wavelength was arranged between apolarizing plate and a reflector such that the angle formed between itsslow axis and absorption axis was 135°, and the azimuth angle of a 30°incidence and 0° light-reception was varied.

When the angle formed between the slow axis and absorption axis is 135°,the polarization azimuth deviates in the opposite direction to the caseof 45°, so that the reflection intensity is minimum in azimuthsdeviating by +15° from the respective azimuths. Hence, the axisplacement is rotated −15°, whereby the reflection intensity becomesminimum in the directional azimuth.

FIG. 25 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 270°, and the incident angle and therotation angle of the axis placement were varied.

When the axis placement is rotated −15° in the opposite direction todeviation, leaking light is minimized, and when the rotation is within arange not less than −25° nor greater than 0°, the reflection intensitybecomes low as compared to that before the rotation so that improvementeffects can be expected. Accordingly, a polarizing plate and aretardation plate having a retardation of about a quarter of the visiblelight wavelength in the substrate in-plane direction are arranged suchthat the angle formed between an azimuth φ in which the reflectionintensity is maximum and an absorption axis P of the polarizing plate isnot less than about 90° nor greater than about 115°, and the angleformed between a slow axis F₁ of the retardation plate and P is about135°, whereby the contrast ratio is improved in the directional azimuth,so that display becomes easy to view. The reason why the angle formedbetween φ and P is set here to not less than 90° nor greater than 135°is that although an angle of 105° is optimal as the embodiment, an anglewithin this range allows the reflection intensity to be low as comparedto that before the rotation, so that improvement effects can beexpected.

FIG. 26 is a perspective view showing a configuration of a polarizingplate+broadband λ/4 and a measurement method. Here, only a reflector, aλ/4 plate, a λ/2 plate, and the polarizing plate are shown in FIG. 26for convenience.

The λ/2 plate and the polarizing plate were arranged such that the angleformed between a slow axis of the λ/2 plate and an absorption axis ofpolarizing plate was 0° to 25°, and the reflection intensity wasmeasured with the azimuth angle of a 30° incidence varied. Here, thebroadband λ/4 is made by layering a first retardation plate having aretardation of about λ/4 (Sumitomo Chemical Co., Ltd., in-planeretardation of 128 nm to 138 nm) and a second retardation plate having aretardation of about λ/2 of the visible light wavelength (SumitomoChemical Co., Ltd., in-plane retardation of 265 nm to 280 nm).

FIG. 27 is a characteristic diagram showing how the reflection intensitychanges in a 270° azimuth with the angle formed between a slow axis of aλ/2 plate and an absorption axis of a polarizing plate changed for everycombination of the λ/2 plate and a λ/4 plate.

In a combination of 275 nm and 138 nm, the reflection intensity becomesminimum in the directional azimuth by setting the angle formed betweenthe slow axis of the λ/2 plate and the absorption axis of the polarizingplate to 5°. Though the axis placement of the λ/4 plate is not mentionedhere, it is only required to place the λ/4 plate such that thepolarization azimuth of linearly polarized light incident from theazimuth of the transmission axis is rotated with the λ/2 plate as asymmetrical axis and the resultant azimuth is 45° or 135° with respectto the slow axis of the λ/4 plate. For example, where the angle formedbetween the slow axis of the λ/2 plate and the absorption axis of thepolarizing plate is 10°, the angle formed between the slow axis of theλ/4 plate and the absorption axis of the polarizing plate becomes 65° or155°. On the other hand, in combinations of 265 nm and 138 nm, and 275nm and 148 nm, the reflection intensity becomes minimum where the angleformed between the slow axis of the λ/2 plate and the absorption axis ofthe polarizing plate is 10°, and accordingly the optimal angle differsdepending on the combination of retardation plates in use. However, anangle of 0° to 20° allows the reflection intensity to be low as comparedto that of the single λ/4 plate, so that improvement effects can beexpected.

Accordingly, this retardation plate is constituted of a firstretardation plate having a retardation of about a quarter of the visiblelight wavelength and a second retardation plate having a retardation ofabout a half of the visible light wavelength, and arrangement is madesuch that the angle formed between a slow axis F₁₂ of the secondretardation plate and the absorption axis P of the polarizing plate isnot less than about 0° nor greater than about 20°, the angle formedbetween a slow axis F₁₁ of the first retardation plate and F₁₂ is notless than about 45° nor greater than about 65° (when the slow axis ofthe combined vector is at about 45°), or not less than about 135° norgreater than about 155° (when the slow axis of the combined vector is atabout 135°), whereby the contrast ratio is improved in the directionalazimuth, so that display becomes easy to view. The reason why the angleformed between F₁₂ and the absorption axis P is set to 0° to 20° is thatwhen the retardation of the retardation plate in use deviates by about10 nm, the optimal angle range deviates by about 5°, and an angle withinthis range allows the reflection intensity to be low as compared to thatof the single λ/4 plate, so that improvement effects can be expected.

FIG. 28 is a perspective view showing an axis placement when uniaxiallystretched films are layered.

The uniaxially stretched film in use here is a λ/4 plate having anin-plane retardation of 138 nm (manufactured by Sumitomo Chemical Co.,Ltd.) and has a retardation of 60 nm to 90 nm in the substrate verticaldirection. Light leakage occurs in azimuths different from those of theslow axes of the uniaxial films.

FIG. 29 is a perspective view showing a configuration of a polarizingplate+λ/4+a compensation plate and a measurement method.

The λ/4 plates as a compensation plate were arranged in layers such thattheir slow axes were at 0° and 90°, and the reflection intensity wasmeasured with the azimuth angle of a 30° incidence varied. Besides, theintensities of configurations, as comparative examples, with and withoutusing as a compensation plate a biaxially stretched film having anin-plane retardation of 2 nm to 3 nm and a retardation in the substratevertical direction of 150 nm (manufactured by Sumitomo Chemical Co.,Ltd.) were similarly measured. In this arrangement, the angle formedbetween the directional azimuth and the slow axis of the uniaxiallystretched film was 0 to 40°, and the reflection intensity was measuredwith an azimuth angle of a 30° incidence.

FIG. 30 is a characteristic diagram showing azimuth anglecharacteristics of every compensation plate.

When the uniaxially stretched film is used as a compensation plate,light greatly leaks in azimuths different from that of the slow axis,and the reflection intensity is minimum in the azimuths of the slowaxes, that is, the directional azimuths, thus showing compensationeffects equivalent to that by a biaxially stretched retardation plate.The leaking light becomes less prominent by decreasing the reflectionintensity in azimuths other than the directional azimuths by thereflecting projections and depressions. In this case, uniaxialstretching shows compensation effects equivalent to that of biaxialstretching in the directional azimuths. Reflection intensity in azimuthsother than the directional azimuths decreases by reflecting projectionsand depressions, so that azimuth dependence can be decreased.

FIG. 31 is a characteristic diagram showing incident anglecharacteristics of the reflection intensity measured when theobservation azimuth was fixed to 270°, and the incident angle and theangle formed between a slow axis of a uniaxially stretched film and adirectional azimuth were varied.

The reflection intensity is minimum at a formed angle of 0°, but wherethe angle is up to 30°, improvement effects can be expected as comparedto the case without compensation. Accordingly, another retardation platehaving retardations in the substrate vertical direction and thesubstrate in-plane direction is arranged in layers on the liquid crystallayer side of the aforesaid retardation plate such that the angle formedbetween an azimuth φ in which the reflection intensity is maximum and aslow axis F₂ of at least one of the retardation plates is not less thanabout 0° nor greater than about 30°, whereby the retardation of theliquid crystal layer due to an oblique incidence can be canceled toimprove the contrast ratio in the directional azimuth, so that thedisplay becomes easy to view. The reason why the retardation plate isarranged on the liquid crystal layer side here is to cancel theretardation of the liquid crystal layer without being affected by theother retardation plate, and the reason why the angle formed between φand F₂ is set to not less than 0° nor greater than 30° is that an angleof 0° is optimal as the embodiment, but where the angle is within therange of not less than 0° nor greater than 30°, improvement in thecontrast ratio in the directional azimuth can be expected.

FIG. 32 is a characteristic diagram showing results of the reflectionintensity in polar angle directions measured, as in FIG. 31, when theliquid crystal alignment on the substrate side where no reflectingprojections and depressions were formed was varied within a range 0° to90° with respect to the directional azimuth.

The reflection intensity is minimum at an angle formed between thealignment azimuth of the liquid crystal and the directional azimuth of90°, but where the angle is 45° or greater, sufficient improvementeffects as compared to the case of parallel alignment can be expected.

FIG. 33 is a schematic view showing a plane shape of a directionalreflector used in this embodiment.

The directional reflector is made by forming continuous projections anddepressions in the shape of protrusions using a resist on a glasssubstrate, and depositing an aluminum film on the surface. The tiltsurfaces of the reflecting projections and depressions are orientedtoward almost the directional azimuths (90° azimuth and 270° azimuth) inwhich the reflection intensity is maximum. Since the reflectingprojections and depressions function as conductive protrusions, theazimuth in which the liquid crystal initially tilts and the azimuth inwhich the liquid crystal is tilt-aligned due to an oblique electricfield are opposite, so that the liquid crystal is aligned in an azimuthdifferent by about 90° from the directional azimuth. A directionalreflector and a non-directional reflector were used to producereflection-type liquid crystal elements. Here, rubbing was performed ina 0° azimuth only for the opposite substrate, and liquid crystal havinga negative dielectric constant anisotropy (manufactured by Merck KGaA)was injected.

The polarizing plate, retardation plates, reflection-type liquid crystalelement were arranged in layers in the configuration shown in FIG. 29,and the contrast ratio was measured in the directional azimuth withrespect to a 30° incidence. The contrast ratio of the reflection-typeliquid crystal display device using the directional reflector was about1.5 times that of a reflection-type liquid crystal display device usingthe non-directional reflector. The retardation of the initially alignedliquid crystal is canceled because the azimuth in which the liquidcrystal is tilt-aligned due to the reflecting projections anddepressions and the azimuth in which the liquid crystal is tilt-alignedby the rubbing are different by 90° from each other in thereflection-type liquid crystal display device using the directionalreflector, while the retardation of the initially aligned liquid crystalis not canceled because the azimuth in which the liquid crystal istilt-aligned due to the reflecting projections and depressions is randomin the reflection-type liquid crystal display device using thenon-directional reflector. This greatly affects the contrast ratio.

Besides, in the observation of the alignment performed with the λ/4plate removed, it was found that the alignment was in almost the sameazimuth in the reflection-type liquid crystal display device using thedirectional reflector, while deflection in alignment azimuth, calledφ-deflection, occurred in the reflection-type liquid crystal displaydevice using the non-directional reflector. This shows that thedirectional reflector generated alignment control force to improve thealignment stability.

FIG. 34 is schematic view showing a plane shape of a directionalreflector with slits used in this embodiment.

The directional reflector is made by forming continuous projections anddepressions in the shape of protrusions using a transparent resin(manufactured by JSR Corp.) on a glass substrate, and depositing analuminum film with slits having a width of 3 μm left in the depressions.The reason why the slits are formed here in the depressions is that thereflection intensity is low in this region and that the cell thicknessnecessary for the transmission region can be achieved, and the reasonwhy the slit width is set to 3 μm is that the region where an obliqueelectric field occurs is narrowed to prevent the liquid crystal frombeing aligned in the azimuth vertical to the tilt surface.

A directional reflector with slits was used to produce areflection-type/transmission-type liquid crystal display device. Here,rubbing processing was performed in a 0° azimuth only for the oppositesubstrate, and liquid crystal having a negative dielectric constantanisotropy was injected. In the observation of the alignment performedwith the λ/4 plate removed, it was found that alignment azimuths on andnear the slits were almost the same, and there occurred no φ-deflectioneven though the slits were formed in the directional reflector.

As has been described, in the reflection-type liquid crystal displaydevice according to this embodiment, the contrast ratio can be maximumin an azimuth in which the reflection intensity is maximum due to thereflecting projections and depressions, thereby making it possible torealize display that is easy to view even when light is incident from aspecific azimuth such as in an indoor environment.

Fourth Embodiment

A fourth embodiment will be described below in detail using thedrawings.

FIG. 35A is a characteristic diagram showing azimuth dependence of thereflectance of a polarizing plate+a λ/4 plate, and FIG. 35B is acharacteristic diagram showing azimuth dependence of the reflectance ofa polarizing plate+a broadband λ/4 plate. The reflectance is a valuewith respect to a 30° incidence and 0° light reception (the substratenormal), and the reflector in use is a non-directional reflector havingno azimuthal anisotropy in reflection intensity. In FIG. 35A, anabsorption axis of a polarizing plate (manufactured by Sumitomo ChemicalCo., Ltd.) was placed at 0°, and a slow axis of a λ/4 plate (in-planeretardation of 138 nm, thickness retardation of 53 nm, manufactured bySekisui Chemical Co., Ltd.) was placed at 45°, and in FIG. 35B, theabsorption axis of the polarizing plate was placed at 0°, a slow axis ofa λ/2 plate (in-plane retardation of 275 nm, thickness retardation of130 nm (manufactured by Sekisui Chemical Co., Ltd.)) was placed at 10°,and the slow axis of the λ/4 plate was placed at 65°.

Besides, a λ/4 plate and a λ/2 plate having no wavelength dispersion norretardations in the thickness direction and a λ/4 plate and a λ/2 platehaving wavelength dispersion but no retardations in the thicknessdirection, were set separately to obtain the azimuth dependence ofreflectance by calculation. FIGS. 35A and B show that (1) thereflectance increases depending on the axial azimuth, wavelengthdispersion, and retardation in the thickness direction (Rth) of theretardation plate, and (2) the broadband λ/4 plate has less wavelengthdispersion and its azimuth in which the reflectance is minimum deviatesfrom the azimuth of the polarization axis depending on Rth. Thereflectance increase due to the axial azimuth occurs by no birefringenceexhibited, the reflectance increase due to the wavelength dispersionoccurs by deviation of retardation from λ/4 at wavelengths other than550 nm, and the reflectance increase due to Rth occurs by addition ofnegative retardation. The difference in reflectance between theretardation plate having Rth and the retardation plate having no Rth isthe reflectance increase due to Rth, which is different depending on theazimuth.

FIG. 36 shows schematic plane views showing plane shapes of reflectorsused in this embodiment.

FIG. 36A shows a non-directional reflector in which reflectingprojections and depressions 51 in the shape of dots with tilt surfacesoriented toward all azimuths are formed on pixel electrodes, and FIG.36B shows a directional reflector in which reflecting projections anddepressions 52 in the shape of steps with tilt surfaces oriented towardtop and bottom (90° and 270°) azimuths are formed on pixel electrodes,respectively.

FIG. 37 is a characteristic diagram showing azimuth dependence of thereflectance of a reflector.

A non-directional reflector exhibits a uniform reflectance in allazimuths, while a directional reflector shows a reflectance of twice theabove reflectance in the directional azimuth (90°) and a reflectance of60 percent of the above reflectance in the non-directional azimuths (0°and 180°)

FIG. 38 shows characteristic diagrams each showing azimuth dependence ofthe reflectance of a polarizing plate+a broadband λ/4 plate+a liquidcrystal layer when the in-plane retardation of a λ/4 plate can bechanged between 109 nm and 148 nm, for each reflector (A:non-directional reflector, B: directional reflector).

Here, the liquid crystal layer is produced by bonding substrates withMicro-pearl spacer (manufactured by Sekisui Fine Chemical Co., Ltd.)with a diameter of 3 μm intervening therebetween, and injecting negativetype liquid crystal (Δn=0.0995, manufactured by Merck KGaA) between thesubstrates, and is kept in a state where no voltage is applied. Further,the entire axial placement is rotated 30° to the left to set theabsorption axis of the polarizing plate at 30° so that the reflectanceis minimum in the directional azimuth. Where there is no opticalcompensation plate, Rth increases in the directional azimuth when theretardation of the λ/4 plate is decreased (preferably, to about 110 nmto 120 nm), so that the retardation of the liquid crystal layer iscorrespondingly compensated to decrease the reflectance. In contrast tothe above, Rth decreases in the non-directional azimuth to increase thereflectance, but application of the directional reflector enables thereflectance to be kept unchanged from that before the change of theretardation plate.

FIG. 39 shows characteristic diagrams each showing azimuth dependence ofthe reflectance of a polarizing plate+a broadband λ/4 plate+a liquidcrystal layer when the in-plane retardation of a λ/2 plate can bechanged between 267 nm and 317 nm, for each reflector (A:non-directional reflector, B: directional reflector).

Rth increases in the directional azimuth when the in-plane retardationof the λ/2 plate is increased (preferably to about 300 nm to 320 m), sothat the retardation of the liquid crystal layer is correspondinglycompensated to decrease the reflectance.

FIG. 40 is a characteristic diagram showing, on a directional reflector,azimuth dependence of the reflectance of a polarizing plate+a broadbandλ/4 plate+a liquid crystal layer when the in-plane retardations of botha λ/4 plate and a λ/2 plate can be changed. The reflectance in thedirectional azimuth also decreases by changing the in-plane retardationsof both the λ/4 plate and the λ/2 plate. However, the reflectanceincrease in the non-directional azimuth is more moderate when they areindividually changed.

From the above description, where there is no optical compensationplate, the applicable wavelength of the λ/4 plate is small and theapplicable wavelength of the λ/2 plate is large, whereby the reflectancecan be decreased in the directional azimuth to increase the contrastratio. Here, it is preferable that the applicable wavelength of the λ/4plate is about 440 nm to 480 nm and the applicable wavelength of the λ/2plate is about 600 nm to 640 nm, and that the applicable wavelengths ofthe respective wavelength plates are made different by a range withinless than 200 nm.

FIG. 41 is a characteristic diagram showing azimuth dependence of thereflectance of a polarizing plate for every polar angle.

The azimuths of an absorption axis of the polarizing plate are at 0° and180° here, and it is shown that the reflectance is decreased in theazimuth of the absorption axis as absorption characteristics of thepolarizing plate. The azimuth of a transmission axis of the polarizingplate is arranged within an angle range parallel or nearly parallel tothe directional azimuth in which the reflection intensity is maximum inthis embodiment, but if the azimuth of the absorption axis of thepolarizing plate is arranged within the angle range parallel or nearlyparallel to the directional azimuth, the reflectance in white display isalso decreased. In other words, when the polarizing plate and thebroadband λ/4 plate are rotated 90° from the axial placement of thisembodiment, the magnitude relation between the respective wavelengthplates is reversed, but, in that axial placement, the reflectance inwhite display is decreased in the directional azimuth, leading to lessimproved contrast ratio.

FIG. 42 shows characteristic diagrams each showing azimuth dependence ofthe reflectance of a polarizing plate+a broadband λ/4 plate+an opticalcompensation plate+a liquid crystal layer when the in-plane retardationof a λ/4 plate can be changed between 128 nm and 159 nm, for eachreflector (A: non-directional reflector, B: directional reflector).

Here, an absorption axis of the polarizing plate was placed at 0°, aslow axis of a λ/2 plate was placed at 10°, a slow axis of the λ/4 platewas placed at 65°, and a slow axis of the optical compensation plate(in-plane retardation of 2 nm, thickness retardation of 150 nm,manufactured by Sumitomo Chemical Co., Ltd.) was placed at 65°. In theconfiguration in FIG. 45, the axial placement is not rotated as in thecase where there is no optical compensation plate. This is becauseretardation remaining in the liquid crystal layer causes a positiveretardation in the thickness direction, so that the azimuth in which thereflection intensity is minimum deviates from the azimuth of thepolarization axis, but canceling most of the positive Rth of the liquidcrystal layer by the negative Rth of the optical compensation plateeliminates occurrence of the azimuth deviation.

Where there is an optical compensation plate and most of the retardationof the liquid crystal layer is canceled by the optical compensationplate, the azimuth dependence of the reflectance of the polarizingplate+the broadband λ/4 plate is reflected, so that Rth decreases in thedirectional azimuth when the retardation of the λ/4 plate is increased(preferably, to about 150 nm) to decrease the reflectance. In contrastto the above, Rth increases in the non-directional azimuth to increasethe reflectance, but application of the directional reflector enablesthe reflectance to be kept unchanged from that before the change of theretardation plate.

FIG. 43 shows characteristic diagrams each showing azimuth dependence ofthe reflectance of a polarizing plate+a broadband λ/4 plate+an opticalcompensation plate+a liquid crystal layer when the in-plane retardationof a λ/2 plate can be changed between 240 nm and 285 nm, for eachreflector (A: non-directional reflector, B: directional reflector).

Rth decreases in the directional azimuth when the in-plane retardationof the λ/2 plate is decreased (preferably to about 240 nm to 260 m), sothat the reflectance is decreased.

FIG. 44 is a characteristic diagram showing, on a directional reflector,azimuth dependence of the reflectance of a polarizing plate+a broadbandλ/4 plate+an optical compensation plate+a liquid crystal layer when thein-plane retardations of both a λ/4 plate and a λ/2 plate can bechanged.

Since the reflectance in the directional azimuth increases when thein-plane retardations of both the λ/4 plate and the λ/2 plate arechanged, they should be individually changed.

From the above description, where there is an optical compensationplate, the applicable wavelength of the λ/4 plate is large and theapplicable wavelength of the λ/2 plate is small, whereby the reflectancecan be decreased in the directional azimuth to increase the contrastratio. Here, it is preferable that the applicable wavelength of the λ/4plate is about 600 nm and the applicable wavelength of the λ/2 plate isabout 480 nm to 520 nm, and that the applicable wavelengths of therespective wavelength plates are made different by a range within lessthan 70 nm.

The above also applies to the case in which a λ/4 plate layered in anorthogonal placement is used as the optical compensation plate. Morespecifically, an absorption axis of a polarizing plate is placed at 0°,a slow axis of another (second) λ/2 plate is placed at 10°, a slow axisof a (first) λ/2 plate is placed at 65°, and a slow axis of the λ/4plate is placed at 155°, and the retardation of the λ/2 plate is largeand the retardation of the other λ/2 plate is small, whereby thereflectance can be decreased in the directional azimuth to increase thecontrast ratio. Here, it is preferable that the λ/2 plate has aretardation of about 290 nm because of including the λ/4 plate as theoptical compensation plate and an applicable wavelength of about 580 nm,and the other λ/2 plate has a retardation of about 240 nm to 260 nm andan applicable wavelength of about 480 nm to 520 nm, and that theapplicable wavelengths of the respective wavelength plates are madedifferent by a range within less than 70 nm.

As has been described, in the reflection-type liquid crystal displaydevice according to this embodiment, the contrast can be increased in anazimuth in which the reflection intensity is maximum due to thereflecting projections and depressions, thereby making it possible torealize display that is easy to view even when light is incident from aspecific azimuth such as in an indoor environment.

1. A liquid crystal display device, comprising: a reflecting layer forreflecting incident light; a liquid crystal layer provided on saidreflecting layer, in which alignment of liquid crystal molecules isvertical; and a retardation plate and a polarizing plate provided on afront surface of said liquid crystal layer, wherein said reflectinglayer has projections and depressions formed on a surface thereof, anaverage tilt angle of the projections and depressions being a value ofnot less than 4° nor greater than 6°, and wherein said retardation platehas a negative refractive index anisotropy in a vertical direction to asurface thereof, birefringence in a direction of the thickness, a ratiobetween a retardation Rf thereof and a retardation Rlc of said liquidcrystal layer, Rf/Rlc, being a value of not less than 0.6 nor greaterthan 0.9.
 2. A liquid crystal display device, comprising: a reflectinglayer for reflecting incident light; a liquid crystal layer provided onsaid reflecting layer, in which alignment of liquid crystal molecules isvertical; and a retardation plate and a polarizing plate provided on afront surface of said liquid crystal layer, wherein said reflectinglayer has projections and depressions formed on a surface thereof, anaverage tilt angle of the projections and depressions being a value ofnot less than 7° nor greater than 9°, and wherein said retardation platehas a negative refractive index anisotropy in a vertical direction to asurface thereof, birefringence in a direction of the thickness, a ratiobetween a retardation Rf thereof and a retardation Rlc of said liquidcrystal layer, Rf/Rlc, being a value of not less than 0.5 nor greaterthan 0.8.
 3. A liquid crystal display device, comprising: a reflectinglayer for reflecting incident light; a liquid crystal layer provided onsaid reflecting layer, in which alignment of liquid crystal molecules isvertical; and a retardation plate and a polarizing plate provided on afront surface of said liquid crystal layer, wherein said reflectinglayer has projections and depressions formed on a surface thereof, anaverage tilt angle of the projections and depressions being a value ofnot less than 10° nor greater than 15°, and wherein said retardationplate has a negative refractive index anisotropy in a vertical directionto a surface thereof, birefringence in a direction of the thickness, aratio between a retardation Rf thereof and a retardation Rlc of saidliquid crystal layer, Rf/Rlc, being a value of not less than 0.4 norgreater than 0.7.
 4. The liquid crystal display device according toclaim 1, wherein where refractive indexes in an x direction, a ydirection, and a z direction of said retardation plate are nx, ny, andnz respectively, and a Nz coefficient is defined such thatNz=(nx−nz)/(nx−ny), the Nz coefficient of said retardation plate is 1 orless.
 5. The liquid crystal display device according to claim 1, whereinsaid retardation plate is made by layering a plurality of uniaxiallystretched films which are arranged in layers such that slow axes of therespective uniaxially stretched films are substantially orthogonal. 6.The liquid crystal display device according to claim 1, wherein theliquid crystal molecule of said liquid crystal layer has a negativedielectric constant anisotropy.
 7. A liquid crystal display device,comprising: a reflecting layer for reflecting incident light; a liquidcrystal layer provided on said reflecting layer, in which alignment ofliquid crystal molecules is vertical; and a retardation plate and apolarizing plate provided on a front surface of said liquid crystallayer, wherein said reflecting layer has projections and depressionsformed on a surface thereof and said retardation plate has birefringencein a direction of the thickness, wherein if an average tilt angle of theprojections and depressions is a value of not less than 4° nor greaterthan 6°, then a ratio between a retardation Rf of said reflecting layerand a retardation Rlc of said liquid crystal layer, Rf/Rlc, is a valueof not less than 0.6 nor greater than 0.9; wherein if an average tiltangle of the projections and depressions is a value of not less than 7°nor greater than 9°, then the ratio Rf/Rlc is a value of not less than0.5 nor greater than 0.8, and wherein if an average tilt angle of theprojections and depressions is a value of not less than 10° nor greaterthan 15°, then the ratio Rf/Rlc is a value of not less than 0.4 norgreater than 0.7.
 8. The liquid crystal display device according toclaim 7, wherein where refractive indexes in an x direction, a ydirection, and a z direction of said retardation plate are n_(x), n_(y),and n_(z) respectively, and a N_(z) coefficient is defined such thatN _(z)=(n _(x) −n _(z))/(n _(x) −n _(y)), the N_(z) coefficient of saidretardation plate is 1 or less.
 9. The liquid crystal display deviceaccording to claim 7, wherein said retardation plate is made by layeringa plurality of uniaxially stretched films which are arranged in layerssuch that slow axes of the respective uniaxially stretched films aresubstantially orthogonal.
 10. The liquid crystal display deviceaccording to claim 7, wherein the liquid crystal molecule of said liquidcrystal layer has a negative dielectric constant anisotropy.